This week's Lancet reports a Dutch investigation into the case of a 65-year-old man who collapsed after taking Viagra.

It says the man passed a medical examination before taking the drug and had no high blood pressure, diabetes or previous heart disease.

He also did not smoke and drank moderately.

However, half an hour after taking Viagra, he began to experience severe chest pains.

He was admitted to hospital and diagnosed as having had a heart attack.

He has since made a full recovery.

No risk factors

The researchers, led by Dr J Feenestra of the Dutch Drug Safety Unit, said the man's collapse appeared to have been triggered solely by taking the drug.

He had no risk factors for heart attack and had not even had a chance to test the much-hyped drug before his collapse.

Sexual exertion is recognised as a trigger factor for heart attacks.

Dr Feenestra concluded: "The close temporal relation between ingesting sildenafil [Viagra] and the onset of severe chest pain due to acute myocardial infarction [heart attack]...suggests that sildenafil was causally related."

However, the researchers said the patient may have had existing coronary-artery disease which had not previously been picked up by doctors.

Viagra's manufacturer, Pfizer, says this shows the research is "pure speculation" and accuses the Lancet of publicity-seeking.

A spokesman said: "This concerns a heart attack in one man. Viagra has been given to around three million men and has been extensively studied in clinical trials."

He added that research showed 55% of men who suffered fatal heart attacks had no previous history of heart disease.

Warnings

Viagra was licensed for sale on prescription in the European Union this week.

Viagra was given the all-clear by Europe this week

EU medical advisors believe the drug is generally safe, although they say it should be given on prescription to allow doctors to screen out those patients who may be at risk from taking it.

They say it should not be prescribed for women, people under 18, those who have had strokes or severe heart problems, people with low blood pressure and those with liver problems.

People with other conditions, such as leukaemia and sickle cell anaemia, are also advised that the drug could be an additional health risk.

Deaths

Over 100 deaths around the world are being investigated in connection with the drug.

Most of the victims are elderly men with a history of heart disease, although Pfizer says some also had no previous history of heart disease.

Over two million people have taken the drug without problems.