Men who are not physically fit are more than four times as likely to die of a heart attack as men who are fit, according to a study presented at the annual meeting of the American Heart Assn. in Dallas. Many previous studies have shown that fitness decreases risk factors in heart disease, such as high cholesterol, high blood pressure and obesity. This study shows that men who keep fit also suffer fewer deaths from heart attacks. The study's author, Dr. Lars Ekelund of Duke University Medical Center, said it is the first such study to rely on precise treadmill measurements of the subjects' fitness. Previous studies have depended on the subjects' own assessment of their fitness, he said.