Viagra, used to treat impotence in men, has been found to reduce the harmful effects of stress on the heart, scientists said yesterday.

　　The drug was originally designed as a candidate treatment for heart disease before its effect on genital blood vessels was appreciated.

　　Now researchers at the Johns Hopkins University School of Medicine in Baltimore have measured the strength of heart beats in a group of 35 adult volunteer patients in whom stress was induced with the drug dobutamine. This chemical mimics the effects of emotional or physical stress by increasing the force of heartbeats and boosting the flow of blood in the body, which can lead to permanently raised blood pressure.

　　The men and women were randomly assigned to two groups, either to be treated with Viagra or a placebo. In those given Viagra, the strength of the heart's contractions was reduced by half, from 150 per cent to 75 per cent.

　　Writing in the journal Circulation, Prof David Kass, who led the study, says: "Sildenafil [Viagra] effectively puts a 'brake' on chemical stimulation of the heart. Knowing more about the effects of sildenafil on heart function will allow for safer evaluation of its use as a treatment for heart problems."

　　Dr Charmaine Griffiths, of the British Heart Foundation, said: "Viagra has been a real advance in treating impotence.

　　"The findings that Viagra affects blood pressure are not surprising - before it was known as a successful treatment for impotence, it was actually being researched for lowering effects on blood pressure.

　　"However, if you have a heart condition you should check with your doctor before taking Viagra.

　　"Mixing this drug with other heart medicines or taking it if you have angina [heart pain on exercise] without advice from a health professional or GP can be dangerous for heart patients," she said.