GLP-1 Microdosing and Heart Failure (HFpEF): Breathlessness, Swelling, and What STEP-HFpEF and SUMMIT Found
For years, heart failure with preserved ejection fraction had almost no drug that made people feel better. Then three GLP-1 trials moved symptom scores more than anything before them. Here is what they measured, who they apply to, and why the microdose question is still open.
~50%
OF ALL HEART FAILURE CASES ARE HFPEF, AND MOST PEOPLE WITH IT CARRY EXCESS WEIGHT
+7.8
EXTRA POINTS OF SYMPTOM-SCORE GAIN WITH SEMAGLUTIDE 2.4 MG VS PLACEBO (STEP-HFPEF, NEJM 2023)
38%
LOWER RISK OF CARDIOVASCULAR DEATH OR WORSENING HEART FAILURE WITH TIRZEPATIDE (SUMMIT, NEJM 2025)
Picture a 66-year-old retired teacher who used to walk her dog two miles every morning. Now she stops twice on the way to the end of the street. Her ankles swell by evening, and she sleeps propped on three pillows. Her echocardiogram says her ejection fraction is 60 percent, which sounds normal. Her cardiologist explains that the problem is not how hard her heart squeezes. It is how stiffly it fills.
That condition is heart failure with preserved ejection fraction, or HFpEF. It has become one of the clearest places where GLP-1 medications have been tested in a heart disease and produced results people can feel. This article walks through the STEP-HFpEF and SUMMIT trials, explains why the findings do not extend to every kind of heart failure, and covers the practical issues of diuretics, fluid, and muscle. It keeps a firm line between full-dose trial data and microdose protocols, which no heart failure trial has studied. The teacher is a composite example, not a real patient.
Key takeaways
- •In STEP-HFpEF (NEJM, 2023), semaglutide 2.4 mg weekly improved the KCCQ symptom score by 16.6 points versus 8.7 on placebo over 52 weeks in 529 people with HFpEF and obesity.
- •In SUMMIT (NEJM, 2025), cardiovascular death or a worsening heart failure event occurred in 9.9 percent of people on tirzepatide versus 15.3 percent on placebo over about two years.
- •The benefits apply to heart failure with preserved ejection fraction plus obesity. Liraglutide did not help people with reduced ejection fraction in the FIGHT trial.
- •GLP-1 drugs reduce appetite and thirst, so people on loop diuretics face a higher risk of dehydration and kidney strain and need closer monitoring.
- •No trial has tested a GLP-1 microdose in heart failure, and symptom gains in the full-dose trials rose with the amount of weight lost.
What is HFpEF, and why is excess weight so central to it?
HFpEF is heart failure in which the heart pumps a normal fraction of its blood, usually 50 percent or more, but the left ventricle is stiff and fills under high pressure. That pressure backs up into the lungs, causing breathlessness, and into the veins, causing swelling in the legs and abdomen. HFpEF makes up roughly half of all heart failure, and in the United States most people diagnosed with it are overweight or living with obesity.
Cardiologists now describe an obesity phenotype of HFpEF. Excess body fat raises blood volume, increases the pressure the heart works against, and adds a layer of inflamed epicardial fat that sits on the heart and limits how freely it can expand. Carrying more body weight also makes every step harder for the lungs and leg muscles. Before 2023, the drugs that help heart failure with reduced ejection fraction had shown little or no effect on how HFpEF patients felt. SGLT2 inhibitors such as empagliflozin and dapagliflozin were the first to reduce hospital admissions, but their effect on symptoms was modest.
What did the STEP-HFpEF trials find with semaglutide?
The STEP-HFpEF trials found that semaglutide 2.4 mg weekly roughly doubled the improvement in heart failure symptoms compared with placebo over one year. The first trial, led by Mikhail Kosiborod and published in the New England Journal of Medicine in 2023, enrolled 529 people with HFpEF and a BMI of 30 or more who did not have diabetes. A second trial, STEP-HFpEF DM, published in 2024, enrolled 616 people with the same profile who also had type 2 diabetes.
Both trials used the Kansas City Cardiomyopathy Questionnaire clinical summary score, or KCCQ, as the main outcome. The KCCQ asks about breathlessness, fatigue, swelling, and physical limits, and a change of 5 points is generally considered noticeable to patients. In STEP-HFpEF, the KCCQ score rose by 16.6 points on semaglutide and 8.7 on placebo. In STEP-HFpEF DM, the figures were 13.7 and 6.4.
Change in KCCQ symptom score (points)
STEP-HFpEF and STEP-HFpEF DM at 52 weeks (semaglutide 2.4 mg). SUMMIT at 52 weeks (tirzepatide up to 15 mg). Rounded.
- Placebo
- GLP-1 drug
Placebo groups improved too, which is common in heart failure trials with close follow-up. The gap between bars is the drug effect.
How much weight did people lose, and did they walk farther?
People in STEP-HFpEF lost an average of 13.3 percent of body weight on semaglutide versus 2.6 percent on placebo, and people with diabetes lost 9.8 percent versus 3.4 percent. Weight loss on GLP-1 drugs is usually smaller in type 2 diabetes, a pattern seen across the STEP and SURMOUNT programs.
Body weight change at 52 weeks (%)
Kosiborod MN et al., NEJM 2023 and 2024. Semaglutide 2.4 mg weekly. Rounded.
- Placebo
- Semaglutide
Six-minute walk distance, a standard test of everyday exercise capacity, improved by about 21 metres on semaglutide versus about 1 metre on placebo in STEP-HFpEF. In the diabetes trial, walk distance rose 14 metres on semaglutide and fell 4 metres on placebo. Twenty metres sounds small. For someone who stops twice on the way down the street, it can be the difference between one rest and two.
Change in six-minute walk distance at 52 weeks (metres)
Kosiborod MN et al., NEJM 2023 and 2024. Rounded.
- Placebo
- Semaglutide
In later analyses, people who lost more weight tended to gain more walking distance and more KCCQ points.
Did tirzepatide reduce hospital admissions in the SUMMIT trial?
Tirzepatide reduced the combined risk of cardiovascular death or a worsening heart failure event by about 38 percent in the SUMMIT trial. Milton Packer and colleagues randomized 731 people with HFpEF and a BMI of 30 or more to tirzepatide, titrated up to 15 mg weekly, or placebo, and followed them for a median of about two years. The primary event occurred in 9.9 percent of the tirzepatide group and 15.3 percent of the placebo group, published in the New England Journal of Medicine in 2025.
Cardiovascular death or worsening heart failure event (%)
Packer M et al., NEJM 2025 (SUMMIT, n=731, median follow-up about 2 years). Hazard ratio 0.62.
Most of the difference came from fewer worsening heart failure events. The trial was too small to show a difference in cardiovascular death alone.
A pooled analysis of the STEP-HFpEF program, published in The Lancet in 2024, also found fewer heart failure events on semaglutide, though the total number of events was small and the trials were not designed for that outcome. Taken together, these trials moved GLP-1 drugs from a symptom story to a hard-outcome story in HFpEF with obesity. Our article on cardiovascular and heart health covers the SELECT trial and heart attack and stroke outcomes.
Is the benefit only from weight loss, or is something else going on?
Weight loss explains much of the HFpEF benefit, but lower inflammation and less fluid congestion probably contribute. In STEP-HFpEF, C-reactive protein, a blood marker of inflammation, fell by about 44 percent on semaglutide against about 7 percent on placebo. An echocardiography substudy reported by Scott Solomon and colleagues in 2024 found smaller left atrial volumes and modestly lower filling pressures on semaglutide, which points to less strain on the heart.
Change in C-reactive protein at 52 weeks (%)
Kosiborod MN et al., NEJM 2023 (STEP-HFpEF). Rounded.
Semaglutide trial participants were also more likely to reduce their loop diuretic dose over the year, and less likely to need it increased, than those on placebo. That fits a picture of less fluid overload. Our article on inflammation and longevity looks at the CRP findings across other GLP-1 trials.
Why do the results not apply to heart failure with reduced ejection fraction?
GLP-1 drugs have not helped heart failure with reduced ejection fraction, or HFrEF, in randomized trials. In the FIGHT trial, published by Kenneth Margulies and colleagues in JAMA in 2016, liraglutide given to 300 people recently hospitalized with HFrEF did not improve the main outcome, and there was a non-significant trend toward more readmissions. The LIVE trial of liraglutide in stable HFrEF found no gain in pumping function and a rise in heart rate of about 7 beats per minute.
A weak heart muscle relies more on heart rate to maintain output, and a GLP-1 driven increase in heart rate may be less welcome there. Our article on atrial fibrillation and heart rhythm explains the heart rate effect. The practical point is that the type of heart failure matters. A person who knows they have heart failure but not their ejection fraction should find out before reading the HFpEF trials as good news for them.
Does any of this apply to a GLP-1 microdose?
None of the heart failure results has been tested at microdose levels. STEP-HFpEF used semaglutide 2.4 mg weekly and SUMMIT used tirzepatide up to 15 mg, and in both programs the people who lost the most weight tended to gain the most in symptoms and walking distance. A microdose protocol uses a fraction of those doses and generally produces slower, smaller weight change, so a proportional benefit cannot be assumed.
A lower dose could plausibly suit some people with heart failure better on tolerability. Gentler appetite suppression means fewer days of skipped meals, vomiting, or diarrhea, which matter more when a person also takes a diuretic. Smaller doses may produce a smaller heart rate rise. Those are reasoned guesses, not trial results. Our microdosing guide covers typical dose ranges, and any heart failure patient considering one needs the heart failure team involved from the start.
What should people with heart failure watch for on a GLP-1?
People with heart failure on a GLP-1 should watch daily weight, hydration, kidney function, and muscle strength. Loop diuretics such as furosemide or torsemide already push fluid out. A GLP-1 that reduces thirst and causes nausea can tip the balance toward dehydration, low blood pressure, and short-term kidney injury. Many heart failure teams check kidney function and electrolytes within a few weeks of a GLP-1 start or dose change and review the diuretic dose as weight falls.
Muscle is the other concern. Heart failure already speeds muscle loss, and rapid weight loss can take lean mass with it. Weakness in the legs worsens exercise capacity, the very thing HFpEF patients want to improve. Adequate protein and some resistance work, cleared by the cardiologist or a cardiac rehab program, help protect it. Our articles on muscle preservation and hydration and micronutrients go further. Daily weights help sort out what is happening:
| What you notice | What it may mean | What to do |
|---|---|---|
| Weight down slowly over weeks, ankles unchanged or less puffy | Expected fat loss, possibly some fluid loss | Keep logging. Share the trend at the next visit. |
| Weight down 1 kg or more in a day or two, with dizziness or dark urine | Possible dehydration, especially on a loop diuretic | Contact the heart failure team the same day. Diuretic dose may need review. |
| Weight up 1 to 1.5 kg in a day or 2 kg in a week | Possible fluid build-up | Call the heart failure team or nurse line promptly. |
| New swelling, needing more pillows, or waking up breathless | Possible worsening heart failure | Same-day medical review. |
| Breathless at rest, chest pain, or fainting | Emergency | Call emergency services. |
The teacher from the introduction fits the trial population closely: HFpEF, a BMI above 30, and symptoms that limit her day. Her cardiologist might reasonably discuss a full-dose GLP-1 alongside an SGLT2 inhibitor, a diuretic plan, and cardiac rehab. A microdose would be an off-label choice with no heart failure data behind it, and that conversation belongs in the clinic.
What is the takeaway?
The takeaway is that full-dose semaglutide and tirzepatide have produced the largest symptom gains yet seen in heart failure with preserved ejection fraction and obesity, and tirzepatide reduced worsening heart failure events in SUMMIT. Those results do not extend to reduced ejection fraction, where liraglutide did not help. People on diuretics need closer fluid and kidney monitoring. At microdose levels, nothing in heart failure has been tested.
"Know your ejection fraction before you read the trials. HFpEF and HFrEF are different diseases with different GLP-1 evidence."
Frequently asked questions
What is HFpEF?
HFpEF stands for heart failure with preserved ejection fraction. The heart pumps out a normal share of its blood with each beat, usually 50 percent or more, but the muscle is stiff and fills poorly, so pressure backs up into the lungs and legs. HFpEF accounts for about half of all heart failure cases, and most people with it are overweight or living with obesity.
Is semaglutide approved for heart failure?
Semaglutide is not approved as a treatment for heart failure itself. The STEP-HFpEF trials tested semaglutide 2.4 mg weekly in people with obesity-related HFpEF and found better symptom scores, more weight loss, and longer walking distance than placebo. Any use in a person with heart failure belongs under the care of their cardiologist or heart failure team.
What did the SUMMIT trial show for tirzepatide?
SUMMIT, published in the New England Journal of Medicine in 2025, randomized 731 people with HFpEF and obesity to tirzepatide or placebo for a median of about two years. Cardiovascular death or a worsening heart failure event occurred in 9.9 percent of the tirzepatide group and 15.3 percent of the placebo group. Symptom scores also improved more with tirzepatide.
Do GLP-1 drugs help heart failure with reduced ejection fraction?
GLP-1 drugs have not shown benefit in heart failure with reduced ejection fraction, where the heart pumps weakly. The FIGHT trial of liraglutide in 300 people recently hospitalized with reduced ejection fraction found no improvement in its main outcome, and the LIVE trial found a rise in heart rate. The positive results so far apply to HFpEF with obesity.
Does a GLP-1 microdose help HFpEF?
No trial has tested a GLP-1 microdose in heart failure. STEP-HFpEF used semaglutide 2.4 mg and SUMMIT used tirzepatide up to 15 mg, and the symptom gains tracked closely with how much weight people lost. A microdose usually produces smaller, slower weight change, so the full-dose results cannot be assumed to carry over.
Can a GLP-1 cause dehydration in someone taking diuretics?
GLP-1 drugs lower appetite and thirst and can cause nausea, vomiting, or diarrhea, which adds to the fluid loss from loop diuretics such as furosemide. That combination can lead to dizziness, low blood pressure, and short-term kidney injury. People with heart failure on diuretics usually need closer weight and kidney monitoring when a GLP-1 starts or the dose changes.
Why do heart failure patients weigh themselves daily?
Daily weights are the simplest early warning for fluid build-up in heart failure. A gain of about 1 to 1.5 kg in a day or 2 kg in a week often signals fluid rather than fat and can appear before breathlessness worsens. On a GLP-1, daily weights also help separate steady fat loss from sudden drops that suggest dehydration.
How does losing weight ease HFpEF symptoms?
Weight loss eases HFpEF symptoms by reducing the work of breathing and moving, lowering blood volume and filling pressures, and shrinking fat around the heart that stiffens it. In STEP-HFpEF, people who lost more weight saw larger gains in symptom scores and walking distance. Lower inflammation, shown by a drop in C-reactive protein of about 44 percent, may also contribute.
Clinical references
- Kosiborod MN, Abildstrøm SZ, Borlaug BA, et al. Semaglutide in patients with heart failure with preserved ejection fraction and obesity (STEP-HFpEF). New England Journal of Medicine. 2023;389(12):1069-1084.
- Kosiborod MN, Petrie MC, Borlaug BA, et al. Semaglutide in patients with obesity-related heart failure and type 2 diabetes (STEP-HFpEF DM). New England Journal of Medicine. 2024;390(15):1394-1407.
- Packer M, Zile MR, Kramer CM, et al. Tirzepatide for heart failure with preserved ejection fraction and obesity (SUMMIT). New England Journal of Medicine. 2025;392(5):427-437.
- Butler J, Shah SJ, Petrie MC, et al. Semaglutide versus placebo in people with obesity-related heart failure with preserved ejection fraction: a pooled analysis of the STEP-HFpEF and STEP-HFpEF DM randomised trials. The Lancet. 2024;403(10437):1635-1648.
- Solomon SD, Ostrominski JW, Wang X, et al. Effect of semaglutide on cardiac structure and function in patients with obesity-related heart failure. Journal of the American College of Cardiology. 2024;84(17):1587-1602.
- Margulies KB, Hernandez AF, Redfield MM, et al. Effects of liraglutide on clinical stability among patients with advanced heart failure and reduced ejection fraction (FIGHT). JAMA. 2016;316(5):500-508.
- Jorsal A, Kistorp C, Holmager P, et al. Effect of liraglutide on left ventricular function in stable chronic heart failure patients with and without diabetes (LIVE). European Journal of Heart Failure. 2017;19(1):69-77.
- Heidenreich PA, Bozkurt B, Aguilar D, et al. 2022 AHA/ACC/HFSA guideline for the management of heart failure. Circulation. 2022;145(18):e895-e1032.
Medical disclaimer. This article is for general educational and informational purposes only. It is not medical advice and not a substitute for the cardiologist, heart failure team, prescriber, or clinician responsible for your care. The studies described here used full doses of semaglutide, tirzepatide, or liraglutide, not microdose protocols, and no GLP-1 microdose has been studied in heart failure. Charts are rounded from published trials, and the patient described in this article is a composite example rather than a real person. GLP-1 microdosing is an off-label approach and should only be undertaken under a prescriber's supervision. Never stop, start, or change a diuretic, SGLT2 inhibitor, beta blocker, or any other heart medication on the basis of this article. Breathlessness at rest, chest pain, fainting, or rapidly worsening swelling require urgent medical care.