New research from the ESC Congress 2026 reveals that metformin does not reduce major cardiovascular events in patients with heart failure with reduced ejection fraction, challenging previous observational hints of cardioprotective effects.
At the ESC Congress 2026 in Madrid, researchers reported that metformin did not reduce the risk of major cardiovascular events in people with heart failure with reduced ejection fraction who also had type 2 diabetes, prediabetes or were at elevated risk of diabetes. The findings came from the Met-HeFT trial, a double-blind study run across 23 centres in Denmark as part of the DANHEART programme. According to the American College of Cardiology, the results were presented alongside a separate meta-analysis that pointed in the same direction.
The trial enrolled 940 people with symptomatic chronic heart failure and a left ventricular ejection fraction of up to 40%, with a mean age of 70 and 16% women. Over an average follow-up of 3.7 years, metformin made no significant difference to the combined outcome of death, worsening heart failure, acute myocardial infarction or stroke compared with placebo. The treatment also failed to shift secondary measures such as all-cause mortality, unplanned heart failure events, new-onset diabetes or NT-proBNP, a blood marker of cardiac stress, according to the trial report.
Professor Henrik Wiggers of Aarhus University Hospital said the study addressed a long-running uncertainty, as earlier observational work had hinted that metformin might offer heart benefits beyond blood sugar control. But he also noted an important limitation: only about 10% of participants had established type 2 diabetes, likely because many patients were already taking metformin before enrolment and were reluctant to stop it. That left the study population weighted more heavily towards people with prediabetes and insulin resistance.
A companion analysis led by Anders Hostrup Larsen of Goedstrup Hospital pooled randomised placebo-controlled trials in heart failure and ischaemic heart disease, including Met-HeFT. It too found no significant cardiovascular benefit from metformin in heart failure with reduced ejection fraction, and no meaningful effect in established ischaemic heart disease. Wiggers said metformin still has a clear role as a glucose-lowering medicine, but the new evidence does not support the idea that it provides independent cardioprotective effects.
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