Laughter may after all be the best medicine. Comedy can make the blood vessels expand, step up the blood flow and leave viewers in good heart, a US heart scientist said yesterday.

Conversely a stressful film can cause a potentially unhealthy narrowing of the arteries.

Michael Miller, a cardiologist at the University of Maryland medical centre, told heart scientists meeting in Orlando, Florida, that he had shown 20 healthy non-smoking volunteers with an average age of 33 two films within 48 hours.

One was a 1996 MGM comedy called Kingpin, rated PG-13 for its crude, sex-related humour. The other was Steven Spielberg's 1998 Saving Private Ryan, set in the chaos of the D-Day landings in Normandy.

The volunteers watched a 15-minute segment of each film lying down in a temperature controlled room. Grim moments on the battlefield had a bad effect on 14 of the 20 volunteers: their blood flow fell by 35% afterwards.

On the other hand, bawdy comedy in a bowling alley put 19 of the 20 on the road to health: blood flow increased by 22%.

"Given the results, it is conceivable that laughing may be important to reduce the risk of cardiovascular disease," Prof Miller said.