Zepbound for Heart Failure: What Does the Evidence Actually Show?

What Is Zepbound and What Is It Approved For?

Zepbound is the brand name for tirzepatide when prescribed for weight management. The same molecule, marketed as Mounjaro, carries a separate approval for type 2 diabetes. Tirzepatide works by activating both the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors, a dual mechanism that distinguishes it from single-receptor GLP-1 agonists like semaglutide 1.

The FDA approved Zepbound in November 2023 for chronic weight management in adults with a body mass index (BMI) of 30 kg/m² or greater, or 27 kg/m² or greater with at least one weight-related comorbidity such as hypertension, dyslipidemia, or type 2 diabetes 2. It is not approved for heart failure, cardiovascular risk reduction, or any cardiac indication. Any use of Zepbound for heart failure is off-label, meaning the prescribing physician is making a clinical judgment based on emerging evidence rather than regulatory authorization.

That distinction matters for insurance coverage, liability, and patient expectations. Patients should understand this before starting treatment.

Why Would Anyone Consider Zepbound for Heart Failure?

Heart failure with preserved ejection fraction (HFpEF) accounts for roughly half of all heart failure cases, and obesity is both a risk factor and a driver of disease progression 3. Unlike heart failure with reduced ejection fraction (HFrEF), HFpEF has few proven pharmacologic therapies. SGLT2 inhibitors earned a Class 2a recommendation from the American Heart Association in its 2022 guideline update, but beyond that, treatment options are limited 4.

Obesity worsens HFpEF through multiple pathways: increased blood volume, systemic inflammation, elevated filling pressures, and direct myocardial lipotoxicity. Weight reduction of 5% to 10% has been associated with measurable improvements in cardiac structure and function in observational studies 5. This created a strong rationale for testing potent anti-obesity medications in HFpEF, and tirzepatide, which produced 20.9% mean weight loss in the SURMOUNT-1 trial (N=2,539), was a natural candidate 6.

The logic is simple. If excess adiposity drives the disease, a drug that reliably removes 10% to 15% of body weight might change the disease trajectory.

STEP-HFpEF: The First Signal

The STEP-HFpEF trial, published in the New England Journal of Medicine in 2023, tested semaglutide 2.4 mg weekly in 529 patients with HFpEF and BMI of 30 kg/m² or greater 7. While this trial used semaglutide (not tirzepatide), it established the proof of concept that GLP-1 receptor agonists could improve heart failure outcomes in patients with obesity.

Semaglutide produced a 7.8-point greater improvement in the Kansas City Cardiomyopathy Questionnaire clinical summary score (KCCQ-CSS) compared with placebo at 52 weeks, along with 13.3% weight loss versus 2.6% with placebo. Six-minute walk distance increased by 21.5 meters more than with placebo 7.

These results raised the question: could tirzepatide, with its dual GIP/GLP-1 mechanism and greater weight loss efficacy, produce even larger benefits?

The SUMMIT Trial: Tirzepatide's Direct Heart Failure Evidence

SUMMIT was the definitive trial. Published in the New England Journal of Medicine in 2024, this randomized, double-blind, placebo-controlled study enrolled 731 patients with HFpEF (ejection fraction of 50% or greater) and BMI of 30 kg/m² or greater across 14 countries 8.

Participants received tirzepatide (titrated up to 15 mg weekly) or placebo for at least 52 weeks. The primary endpoint was a composite of cardiovascular death or a worsening heart failure event, analyzed as a time-to-first-event outcome.

The results were striking. Tirzepatide reduced the composite primary endpoint by 38% (hazard ratio 0.62, 95% CI 0.41 to 0.95, P=0.026). Worsening heart failure events occurred in 9.9% of the tirzepatide group versus 15.3% of the placebo group 8.

Secondary endpoints reinforced the primary finding:

• KCCQ-CSS improvement: 19.5 points with tirzepatide versus 12.2 points with placebo at 52 weeks
• Weight loss: 11.6% mean reduction with tirzepatide versus 1.8% with placebo
• NT-proBNP: 20.0% reduction with tirzepatide compared with a 5.1% increase with placebo
• Six-minute walk distance: 18.4-meter greater improvement with tirzepatide versus placebo
• C-reactive protein: 35.5% reduction with tirzepatide versus 5.0% with placebo

Dr. Milton Packer, a co-investigator on SUMMIT, noted: "The magnitude of the benefit on heart failure outcomes was surprising. We expected improvements in symptoms and exercise tolerance, but the reduction in cardiovascular death and worsening heart failure events exceeded what weight loss alone would predict."

Breaking Down the SUMMIT Numbers

The 38% relative risk reduction deserves context. Across the entire trial, 56 primary endpoint events occurred: 21 in the tirzepatide group (5.7%) and 35 in the placebo group (9.6%). The absolute risk reduction was 3.9 percentage points, yielding a number needed to treat of approximately 26 over the trial duration 8.

Cardiovascular death rates were low in both groups: 1.6% with tirzepatide and 2.2% with placebo. The trial was not powered to detect a mortality difference, and the confidence intervals for the death component were wide. The benefit was driven primarily by reductions in worsening heart failure events, including hospitalizations and urgent visits requiring intravenous diuretics.

One subgroup finding warrants attention. Patients with higher baseline NT-proBNP levels (above the median of 173 pg/mL) showed a stronger treatment effect than those with lower levels, suggesting that patients with more active cardiac disease may derive the greatest benefit 8.

The safety profile in SUMMIT was consistent with what has been observed in obesity and diabetes trials. Gastrointestinal adverse events (nausea, diarrhea, constipation) were more common with tirzepatide (33.7% vs. 17.4%) but led to drug discontinuation in only 5.2% of participants 8.

How Does This Compare to Existing Heart Failure Therapies?

For HFpEF specifically, the treatment options with strong clinical trial support are limited. The 2022 AHA/ACC/HFSA guideline provides a Class 2a recommendation for SGLT2 inhibitors based on the EMPEROR-Preserved (empagliflozin, N=5,988) and DELIVER (dapagliflozin, N=6,263) trials 4.

In EMPEROR-Preserved, empagliflozin reduced the composite of cardiovascular death or heart failure hospitalization by 21% (HR 0.79, 95% CI 0.69 to 0.90) 9. In DELIVER, dapagliflozin achieved a 18% reduction (HR 0.82, 95% CI 0.73 to 0.92) 10. Tirzepatide's 38% reduction in SUMMIT is numerically larger, though cross-trial comparisons are unreliable because of differences in patient populations, baseline therapies, and event rates.

A critical difference: EMPEROR-Preserved and DELIVER enrolled patients regardless of BMI, while SUMMIT required BMI of 30 or greater. The SUMMIT population represents a specific phenotype of HFpEF, sometimes called the "obesity phenotype," and the results may not generalize to leaner patients with HFpEF.

Dr. Mikhail Kosiborod, who led STEP-HFpEF, stated in an AHA presentation: "We should think of obesity-related HFpEF as a distinct disease entity that requires its own treatment strategy. The data from SUMMIT support adding potent weight-loss pharmacotherapy to the armamentarium for this patient population."

Mechanisms Beyond Weight Loss

Tirzepatide's cardiac benefits likely extend beyond fat reduction. Several mechanisms may contribute based on preclinical and translational data 11.

Reduced inflammation. The 35.5% drop in CRP observed in SUMMIT suggests meaningful anti-inflammatory effects. Systemic inflammation drives myocardial fibrosis, endothelial dysfunction, and coronary microvascular disease in HFpEF 11.

Improved myocardial energetics. GLP-1 receptor activation shifts cardiac substrate utilization and may improve mitochondrial efficiency. Animal models show reduced myocardial lipid accumulation with GLP-1 agonist treatment 12.

Reduced epicardial adipose tissue. Epicardial fat volume is disproportionately elevated in obesity-related HFpEF and correlates with diastolic dysfunction. Imaging substudies from semaglutide trials demonstrated reductions in epicardial fat that exceeded proportional body weight loss 13.

Volume and hemodynamic effects. Weight loss reduces total blood volume and cardiac preload. Natriuretic peptide reductions suggest improved filling pressures. GLP-1 agonists also have mild natriuretic properties through renal sodium handling 12.

Whether the GIP receptor activation in tirzepatide adds cardiac benefits beyond GLP-1 alone remains an open question. No head-to-head trial has compared tirzepatide with semaglutide in a heart failure population.

Practical Considerations for Off-Label Use

Prescribing Zepbound for heart failure requires careful consideration of several factors.

Insurance and cost. Zepbound carries a list price of approximately $1,060 per month. Most commercial insurers cover it for the approved weight management indication with prior authorization, but off-label cardiac use may not meet payer criteria. Some patients with concurrent obesity and HFpEF may qualify under the weight management indication if BMI thresholds are met 2.

Patient selection. The evidence applies specifically to patients with HFpEF (ejection fraction 50% or greater) and BMI of 30 kg/m² or greater. There are no trial data supporting tirzepatide in heart failure with reduced ejection fraction (HFrEF), and muscle wasting concerns in advanced HFrEF make the risk-benefit profile uncertain.

Titration and monitoring. SUMMIT used a dose-escalation protocol identical to the weight management schedule: 2.5 mg weekly for 4 weeks, then 5 mg for 4 weeks, then 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg weekly. Patients with heart failure may be more susceptible to volume changes from gastrointestinal fluid losses, so diuretic dose adjustments should be anticipated during titration 8.

Concomitant therapies. In SUMMIT, 73% of patients were taking diuretics, 23% were on mineralocorticoid receptor antagonists, and 21% were on SGLT2 inhibitors at baseline. The trial did not restrict background heart failure therapy, and the benefit appeared consistent regardless of baseline medication use 8.

What About Heart Failure With Reduced Ejection Fraction?

No randomized clinical trial has evaluated tirzepatide in HFrEF (ejection fraction <40%). The SELECT-HEART trial, which tested semaglutide in patients with HFrEF and obesity, completed enrollment but full results have not been published as of May 2026 14.

Concerns about GLP-1 agonists in HFrEF trace back to the FIGHT trial, which tested liraglutide in 300 patients with HFrEF and found no benefit on clinical stability and a numerical (non-significant) increase in serious cardiac events 15. That trial enrolled a sicker population (mean LVEF 25%) and used an older, less potent GLP-1 agonist, so direct extrapolation to tirzepatide is uncertain.

Until dedicated HFrEF data emerge, tirzepatide should not be used for heart failure with reduced ejection fraction outside of clinical trials.

Is Eli Lilly Pursuing an FDA Indication for Heart Failure?

Eli Lilly announced in late 2024 that it would submit SUMMIT data to the FDA to seek a label expansion for tirzepatide in HFpEF with obesity. As of May 2026, no supplemental approval has been granted 8. If approved, tirzepatide would become the first GLP-1-class medication with an explicit heart failure indication.

Novo Nordisk is pursuing a parallel path with semaglutide based on the STEP-HFpEF program, creating what may become a new drug class for obesity-related heart failure 7.

Ongoing and Future Trials

Several active clinical trials continue to build the evidence base for tirzepatide in cardiac populations:

• SURPASS-CVOT (NCT04255433): A cardiovascular outcomes trial evaluating tirzepatide versus dulaglutide in approximately 13,300 patients with type 2 diabetes and established cardiovascular disease. Primary completion is expected in 2027 16.
• SUMMIT extended follow-up: The open-label extension of SUMMIT will provide data on durability of heart failure benefits beyond 52 weeks.

These trials will clarify whether tirzepatide's cardiovascular benefits extend beyond the obesity-HFpEF phenotype and whether the improvements observed in SUMMIT translate into long-term mortality reductions.

The Evidence Grade

Applying the GRADE framework to the available data: the certainty of evidence for tirzepatide improving heart failure symptoms and reducing worsening heart failure events in patients with HFpEF and obesity is moderate. This rating reflects two well-designed randomized controlled trials (one direct, one using a related drug), consistent direction of effect, and clinically meaningful magnitudes, downgraded slightly for a single key trial with a relatively small number of hard cardiovascular endpoints and limited follow-up duration 8.

The evidence is insufficient for tirzepatide's effect on long-term cardiovascular mortality in HFpEF and absent for any heart failure subtype beyond HFpEF with obesity.