While these figures may seem low for a group of patients whose health has already been seriously compromised, they have to be weighed against the less than 1 per cent mortality rate among patients with similar blockages who were treated conservatively with medication, according to data collated by the Noninvasive Heart Center in San Diego, California (www.heartprotect.com/mortality-stats.shtml).

Not surprisingly, perhaps, the percentage of deaths rises with the age of the patient. In one study of 528 patients over 80 years of age, the 30-day mortality rate was 8.3 per cent, rising to 18 per cent after one year (Ann Thorac Surg, 1994; 58: 445-51).

Other common symptoms following surgery include breathing difficulties, bleeding, infection, depression, hypertension (high blood pressure) and arrhythmias (abnormal heart rhythms). Risk and adverse reactions increase in patients who are older, or have diabetes or other major health problems.

But if you do manage to successfully escape stroke, heart attack, mental problems or death itself, there’s a reasonable chance that bypass surgery won’t improve the health of your heart anyway. A meta-analysis of 37 studies found that heart function improved in only 37-55 per cent of all cases. The rest were neither better nor worse off than before surgery.

One symptom that bypass surgery is supposed to eradicate is recurring angina pectoris, usually caused by arterial blockage. But the same meta-analysis found that up to 20 per cent of bypass patients suffer chest pain even after surgery (J Am Coll Cardiol, 1997; 30: 1451-60).

The self-healing heart It appears that bypass surgery interrupts a self-healing process that the body automatically initiates when it detects that not enough oxygen is reaching the heart. Extraordinarily, 75 per cent of heart patients experience a relief of pain within three to six months without any medical intervention because the body grows new blood vessels to form a natural bypass of the obstructed arteries.

These ‘collateral vessels’, as they are known, can be life-savers as they are able to keep the blood flowing to the heart even when a main artery has completely closed. These collaterals usually disappear after bypass surgery, as the body ‘senses’ a new flow of blood to the heart. But given the reasonable risk that the new grafted vessels may start closing within three months after surgery, the patient may well be left worse off than before.

Collateral vessels tend to grow when arterial narrowing and blocking take place slowly. A vessel that is only slightly narrowed, but which then suddenly blocks completely, is likely to cause a myocardial infarction (heart attack). The body can do nothing to prevent this.

'The common practice of rushing patients in for emergency or urgent surgery because of a severely narrowed coronary artery is completely unnecessary, and needlessly frightens the patient and his family,' says Dr Howard Wayne of the Noninvasive Heart Center.

This view is supported by a study that found that the chances of survival following a mild heart attack are higher if the hospital does not immediately operate, but adopts a conservative approach instead. Overall, 80 of 138 individuals who underwent invasive treatment, such as a bypass, died during a 23-month follow-up period, compared with 59 of 123 patients who had received conservative treatment, including drug therapy (N Engl J Med, 1998; 338: 1785-92).