The best tool for predicting the risk of heart disease may be a tape measure, researchers said on Tuesday.

Studies presented at a meeting of the American Heart Association show that having a big waist may be a fast route to a heart attack or serious heart disease.

“Waist circumference is a vital sign,” said Dr. Robert Eckel, a heart expert at the University of Colorado and president-elect of the American Heart Association.

Doctors check cholesterol levels, blood pressure and obesity to measure the risk of heart disease, by far the No. 1 cause of death in the United States and much of the world. The U.S. Centers for Disease Control and Prevention says 930,000 Americans died of cardiovascular disease in 2001.

Smoking remains the greatest cause of death from heart disease, but obesity is catching up. Statistics have also started to show clearly that where fat goes on the body is important - an “apple” shape with fat in the middle is more dangerous than a bottom-heavy “pear” shape.

Dr. Xavier Jouven of the French research unit INSERM in Villejuif, France, and colleagues studied 7,000 middle-aged French policemen who died of heart attacks or other sudden heart problems between 1967 and 1984.

They looked at waist circumference and body mass index - a ratio of height to weight that is used globally to tell if someone is overweight or obese.

The men with pot bellies were more likely to die suddenly, Jouven told a meeting of the heart association.

“The risk of sudden death increased with abdominal density,” Jouven told a news conference. “The relationship was not observed for nonsudden coronary death.”

And people with higher body mass index were not any more likely to die suddenly unless they also had a big waist.

In the case of men, a 40-inch (102-cm) waist seems to be the dangerous cut-off point. For women the risk starts at 30 inches (76 cm).

Dr. Khawaja Ammar of the Olmsted Medical Center in Rochester, Minnesota, studied 2,000 adults 45 years and older from the area and made several measurements of fatness, including waist circumference, neck circumference, body mass index and skin-fold thickness on the arms and waist.

His team also found that people who had fat in the center of the body were more likely to have specific heart symptoms called left ventricular dysfunction and diastolic dysfunction - measures of how well the heart is pumping.

When they looked at who died over five years, those who had poor diastolic function and who had large waists were much more likely to have died.

“Instead of measuring weight and height and body mass index ... it may be better to measure waist circumference or even neck circumference,” Ammar said.