Want to up your chances of surviving a heart attack? Jump on the treadmill. According to a new study out of Denmark, exercise may increase your chances of surviving a heart attack.

Researchers compared the physical activity levels among 1,664 heart attack sufferers, including 425 who died immediately afterward. Those who had been physically active were more likely to survive the attack.

In fact, the heart patients who regularly engaged in light physical activity were 32 percent less likely to die from a heart attack than sedentary individuals. That number jumped to 47 percent among those who regularly engaged in high physical activity levels.

"We know that exercise protects people against having a heart attack," said study co-author Eva Prescott.

"Animal studies suggest that myocardial infarctions [heart attacks] are smaller and less likely to be fatal in animals that exercise. We wanted to see if exercise was linked with less serious myocardial infarctions in people," she added in a journal news release.

Prescott, a professor of cardiovascular prevention and rehabilitation at the University of Copenhagen, said one possible explanation is that people who exercise may develop collateral blood vessels in the heart. Those vessels ensure the heart continues to get enough blood after a blockage.

“Exercise may also increase levels of chemical substances that improve blood flow and reduce injury to the heart from a heart attack . . . I think it's safe to say that we already knew exercise was good for health and this might indicate that continuing to exercise even after developing atherosclerosis [hardening of the arteries] may reduce the seriousness of a heart attack if it does occur" Prescott said.

But there is a caveat. If you are angry or upset you should avoid an intense workout, according to a large international study that has tied stress and exercise to an increase in heart attack risk.

"This study is further evidence of the connection between mind and body. When you're angry, that's not the time to go out and chop a stack of wood," said Barry Jacobs, a psychologist at the Crozer-Keystone Health System in suburban Philadelphia.

The study, published in the American Heart Association journal Circulation, mirrors earlier studies that have looked at anger and exertion as heart attack triggers. The study involved 12,461 people suffering a first heart attack in 52 countries.

So how often and how long should you exercise? If you're not active or used to exercising, gradually work up to doing 30 minutes of aerobic exercise at least three or four times a week, experts say. The more exercise the better, but any amount is beneficial.

When it comes to which exercises are best, anything that makes your heart beat faster is a great choice. But, exercise should be tailored to your individual needs. If you're looking for a low-impact exercise that's easy on your joints, consider walking, biking, or swimming.

Regardless of which activity you choose, each exercise session should include a warm-up, conditioning, and cool down. During your warm-up, take it easy and let your body get used to the increase in physical activity. Conditioning is the main part of your workout where you should give your maximum exertion. Your cool down is a transition period out of your workout.

Don't sit, stand still or lie down right after exercising; it can cause dizziness and heart palpitations. The best cool-down is to continue with whatever activity you're doing, but at a less intense pace.

In terms of exertion, a cardio workout is considered moderate. A good rule of thumb: If you can talk but not sing during your exercise routine you’re exerting yourself sufficiently, but not overdoing it.

A more vigorous will make it difficult for you to say more than a few words without taking a breath.

Listen to your body when it comes to what's right for you and ask your doctor if there are certain exercises you should avoid.