An exercise treadmill test done within two weeks after a heart attack helps predict the patient's chance of living through the next year, a new study shows.

Twenty-seven percent of heart attack patients whose tests showed an abnormality died within a year, according to a Canadian study published this week in the New England Journal of Medicine. Among patients with normal tests the death rate was only 2 percent.

Although recent research has questioned the use of exercise tests to predict heart disease in patients without overt symptoms, doctors have long found the test valuable for determining how much exercise a patient can safely do after a heart attack.

The Canadian research suggests, however, that even 11 days after a heart attack, the exercise test is a safe way to separate patients into "high risk" and "low risk" groups, said Dr. David D. Waters, one of the Montreal Heart Institute cardiologists who conducted the study.

The researchers conducted a "modified" exercise test on 210 patients 7 to 20 days after a heart attack. Though the test was less demanding than treadmill tests given to healthy patients, Waters said no other study has put this much stress on patients' hearts so soon after a heart attack. No patient suffered any complications from the test, he said, showing that heart patients can do vigorous exercise sooner than many cardiologists have believed.

Though the overall death rate in the first year after a heart attack was 9.5 percent, the researchers found that only 2.1 percent of the 167 patients with a normal exercise test died. Waters said this meant that about two-thirds of patients with an "uncomplicated" heart attack are in a low-risk group, and can probably build up to normal exercise without the need for multiple drugs and extensive further tests.

Sixty-four patients showed changes in their electrocardiograms during the test, indicating that part of the heart was receiving insufficient blood.

Of those patients, 17 were dead one year later, including 10 who died suddenly, presumably of a cardiac arrest.

Waters said that the Canadian cardiologists would now recommend early exercise testing for any heart attack patient under age 70, as long as there had been no chest pain for four days preceding the test and no symptoms of "heart failure" such as shortness of breath or rapid heart rate.

He said cardiologists are now faced with the problem of how to treat the "high risk" patients, since no treatment plan has been proved to increase life span.

For the high risk patients, he said the Canadian researchers favor slower rehabilitation, more frequent use of medicines to decrease demand on the heart, and earlier consideration of bypass surgery on diseased arteries.

Waters said a normal exercise test soon after a heart attack is useful for rehabilitation "because it shows the patient he is not going to be a cardiac cripple the rest of his life." Patients with an abnormal test, he said, often develop chest pain along with their electrocardiogram changes, giving them an indication of how much exercise they can do without danger.

The hardest patient to advise, he said, is the one who has an abnormal test with no pain, because such a patient will have no symptoms to warn him when he overstresses his heart. "We kind of tell them to take it easy, to do no more exercise than they have just done" during the test, Waters said.