According to the British Heart Foundation (BHF), the UK's leading advisory group on heart health, you should make the call if the pains persist for longer than 15 minutes - and that's if you have a known heart problem.

The advice is wrong by at least five minutes, a leading cardiologist has claimed, (and we reckon it's out by 15 minutes). It often takes just 10 minutes from the first symptoms to full cardiac arrest - so the sufferer may no longer be able to make the call within the BHF's timeframe.

Following cardiac arrest, literally every minute counts. The chance of successful defibrillation declines 10 per cent for every minute thereafter, says Dr A Khavandi, a heart specialist at a teaching hospital in Bristol, UK.

If you do have an existing heart problem, your chances of dying from a heart attack are seven times higher than they are for someone who is healthy.

And yet 40 per cent of all heart sufferers are reluctant to call emergency services straight away when they start suffering chest pains, a recent study revealed.

Dr Khavandi suggests this may well be because of the puzzling advice being sent out by the BHF. In a recent campaign aimed at healthy people, its advice was to call the emergency services immediately if anyone starts having chest pains - and yet it tells people with an existing heart condition to wait 15 minutes.

Its mission statement is to see "a world in which people do not die prematurely of heart disease". If it shifts its advice on calling the emergency services from 15 minutes to 15 seconds, it might be a step closer to achieving it.

(Source: British Medical Journal, 2007; 335: 3-4).