A pill for chest pains that costs around £10 per week could save the lives of thousands of heart failure patients. It would also save the NHS millions by reducing hospital admissions by a quarter, trial results have shown.

One expert involved in the trial – the largest so far published on heart failure – described the evidence as a "significant breakthrough" and said it would compel him to change his clinical practice. At a conservative estimate, up to 10,000 deaths per year in the UK could be prevented, he said.

The drug, ivabradine, also known under the brand name Procoralan, is already available in the UK for angina and is known to be safe. The trial results, presented today at the European Society of Cardiology annual meeting in Stockholm and published in the Lancet medical journal, suggest that ivabradine could be resurrected as a cost-effective treatment for many thousands of patients with moderate to severe heart failure.

Over two years, the drug cut the trial patients' risk of death from heart failure by 26%. It had a similar impact on the likelihood of their being admitted to hospital because of worsening symptoms.

More than 700,000 people over the age of 45 live with the risk of heart failure, which occurs when damage to the heart leaves it too weak to pump blood efficiently round the body. An estimated 68,000 cases are diagnosed each year. Heart failure causes fatigue, breathlessness, increased heart rate, and swollen ankles. It can lead to serious complications. Around 40% of those affected are dead after a year.

Heart failure soaks up 1-2% of the total NHS budget; the direct medical costs alone amount to £625m a year.

The trial involved more than 6,500 patients in 37 countries, including Britain, already on standard treatments such as beta-blockers. Participants were randomly assigned additional varying doses of ivabradine, or placed in a "control group" receiving standard treatment only. All the patients had chronic heart failure and a high heart rate of 70 beats per minute or more.

The researchers, led by Professor Karl Swedberg from Sahlgrenska University Hospital in Goteborg, Sweden, wrote: "Ivabradine substantially and significantly reduced major risks associated with heart failure when added to guideline-based and evidence-based treatment."

The key to ivabradine is its effect on heart rate. Unlike other treatments, such as beta-blockers, it lowers the number of heartbeats per minute without also reducing blood pressure.

Prof Martin Cowie, consultant cardiologist at the Royal Brompton hospital in London, who led the UK arm of the study, said: "The evidence represents a significant clinical breakthrough in the management of heart failure and is incredibly important information for patients with this condition. We now know that more lives can be saved and improved simply by adding ivabradine to their current treatment in order to take some of the strain off the heart. It is vital that the results of this study are implemented and ivabradine is used as part of standard heart failure treatment as soon as possible."

At a conservative estimate, prescribing ivabradine to eligible patients could save 5,000 to 10,000 lives a year, he said. Cowie added: "I rarely come back from a conference and say I've got to change my clinical practice, but these results will make me do that. There are lots of patients I'm going to have to discuss this with." He said other international experts he had spoken to were "excited" by the findings.

But one expert cautioned against rushing into treatment with ivabradine. In a comment in the Lancet, Dr John Teerlink, from the University of California in San Francisco, questioned whether all the control-group patients were being optimally treated with standard medications. Those receiving high enough doses of beta-blockers saw no significant extra benefit from ivabradine, he said., adding: "Many unresolved questions about the generalisability of these results and applicability to a broader population of patients can only be addressed in additional clinical trials.".

The British Heart Foundation welcomed the study, saying further trials were now needed to establish the pill's role in heart failure management.