A French study finds that men with a resting pulse of more than 75 beats a minute are a elevated risk of sudden cardiac death. A heart beat that responds sluggishly to exercise is also a danger sign, the researchers found.

The findings, published in the New England Journal of Medicine, are based on a study of 5,713 apparently health working men between the ages of 42 and 53 years. None had been diagnosed with heart disease.

The test subjects underwent standardized testing between 1967 and 1972 and researchers examined data on the subjects' resting heart rates, the increase in rate from the resting level to the peak exercise level, and the decrease in rate from the peak exercise level to the level one minute after the termination of exercise.

During a 23-year follow-up period, 81 subjects died suddenly.

The risk of sudden death was increased in subjects with a resting heart rate that was more than 75 beats per minute and in subjects with an increase in heart rate during exercise that was less than 89 beats per minute, and in subjects with a decrease in heart rate of less than 25 beats per minute after the termination of exercise.

"These three factors (were) strongly associated with an increased risk of sudden death," the researchers said.

The research is the first large study to show an association between so-called heart rate profile and the future risk of sudden cardiac death in healthy people, said lead author Xavier Jouven, a physician at Georges Pompidou European Hospital in Paris.

The test could be useful for men over 40 and women over 50 who have at least two risk factors for heart disease, which may include high cholesterol, high blood pressure, obesity or a family history of heart disease, physicians not associated with the study said.

Sudden cardiac death is responsible for 5 percent to 10 percent of all U.S. deaths, or roughly 350,000 to 500,000 deaths a year. It strikes people as young as their 30s and 40s, often with no prior warning.