A team from Dundee University discovered angina patients who were given allopurinol were able to exercise longer and harder before they experienced chest pain.
They believe the drug to be an inexpensive and safe treatment which may in future reduce the need for surgery and hospital admissions.
But the man leading the research revealed he almost gave up the study after twice being turned down for funding.
Angina is a common disease that causes patients to have a narrowing of their coronary arteries, the blood vessels that supply the heart with oxygen. It affects 6.6 per cent of adult males and 5.6 per cent of adult females in Scotland.
When the arteries are blocked, causing the heart to run out of oxygen, people can suffer chest pain when trying to make the heart work harder by exercising.
The Dundee team, which is publishing its findings in this month's edition of the Lancet, says allopurinol appears to protect the heart against oxygen deficiency. Allan Struthers, professor of cardiovascular medicine at the university's Centre for Cardiovascular and Lung Biology, said the paper is an exciting piece of research which he hopes will be able to increase the quality of life for angina sufferers.
Gout is a type of arthritis which results from an excess of uric acid in the blood and tissues of the body.
This can form into needle-like crystals which can inflame joints and cause severe pain and swelling. In 2008-9 doctors wrote 305,556 prescriptions for gout and allopurinol was dispensed in 289,556 cases.
The drug is used to prevent the build up of uric acid crystals. As uric acid is formed, a byproduct is that oxygen is also used up. The researchers decided to examine the idea that, in preventing the build up of uric acid, the drug would increase the supply of oxygen to the heart.
Prof Struthers said: "That's what led to the idea that, as well as decreasing uric acid to prevent gout, it can perhaps increase oxygen supply and so help angina.
"Allopurinol has been on the market for about 40 years and so it's a cheap drug, one that is obviously very well tolerated with very few side-effects. What we have shown is that it has another property completely different to gout-prevention, which hadn't really been suspected before.
"We live in an age of austerity and finding new uses for old drugs that are cheap and safe is very valuable, especially when a disease is as common as angina."
Prof Struthers said the research was a "blue skies idea" that was rejected by two funding bodies before finally getting approval.
He said the team used 600mg of allopurinol for the angina patients, twice the typical dose for gout patients.
He added: "This could be one of the reasons why no-one stumbled across this effect before as it's usually used at lower doses than we used."
He said a larger-scale study would be necessary to determine the full potential of prescribing allopurinol to angina sufferers.
Professor Peter Weissberg, medical director of the BHF, said: "There are several effective medicines out there for controlling angina, but it's helpful for doctors to have another option."
Few side-effects of pill that has been about for decades
THE drug allopurinol has been the standard treatment for gout since the 1960s.
Almost all long-term gout patients have been treated with allopurinol as a preventative measure because it reduces the amount of uric acid made in the body.
Treatment is usually started with a small dose of 100mg daily and this is gradually increased. Doses over 300mg a day are seldom prescribed, although doses up to 900mg a day are occasionally needed.
It is a highly successful drug. At least half of patients with gout can be treated very effectively with the correct dosage of allopurinol plus attention to lifestyle.
People with gout should slowly and progressively lose weight, reduce their intake of liver, kidney and red meat – asparagus also – and reduce intake of alcohol, particularly beer.
Every prescription of allopurinol should be accompanied by a lifestyle assessment.
Side-effects are very low. There is the occasional person who is idiosyncratically prone to intolerance and comes out in a rash and has liver problems. This is unusual. I have seen only two in 40 years of treating gout. Others who can suffer side effects are those who already have kidney problems.
Dr Michael Snaith is a rheumatologist and trustee of the UK Gout Society.