Heart attack survivors on prescription doses of a group of painkiller called non-steroidal anti-inflammatory drugs (NSAIDs), which include ibuprofen, were 45 per cent more likely to suffer a second attack within a week of the first as those taking none, found Danish researchers.
Those taking one in particular, called diclofenac, were three times more likely to suffer another heart attack within a week of the first.
The results were from a study almost 84,000 Danish heart attack survivors, whose average age was 68. Almost half (42 per cent) were taking a prescription NSAID.
According to the National Institute for Health and Clinical Excellence (Nice), "some standard NSAIDs have been shown to be associated with a small increased risk of heart attack and stroke, especially when used in high doses and for long periods".
But Anne-Marie Schjerning Olsen, from Copenhagen University, who led the study, published in Circulation: Journal of the American Heart Association, said: "What we show is that even for the shortest time periods, these can be dangerous."
For those on prescription ibuprofen - with the average dose being 1,600mg per day - there was no increased risk of a recurrent heart attack within seven days, she said.
However, between eight days and 14 weeks the risk was raised by 50 per cent, compared to taking nothing.
It is not known exactly why NSAIDs increase heart disease risk, although Olsen said they appeared to increase blood clot formation and systemic blood pressure.
*Cardiac patients in hospital should be given blood-pressure lowering drugs in the evening rather than the morning, say Canadian researchers.
Doctors often give angiotensin-converting enzyme (ACE) inhibitors to patients with heart failure or those who have had a heart attack on their morning rounds for convenience.
But the study by Tami Martino and Jeremy Simpson of Guelph University found this was ineffective.
Only giving them in the evening, before sleep, was effective, they found in a study of mice with high blood pressure.
They think the difference is because the heart follows a daily rhythm.
It repairs itself in sleep, and hormones that enlarge the heart peak during these hours as part of this process.
However, in cardiac patients this enlarging activity can cause damage. Giving ACE inhibitors in the evening reduces the nightly hormone peak and subsequently reduce potentially damaging enlargement, they concluded in their study, to be published in the Journal of the American College of Cardiology.