More exercise isn’t always mean better, according to new research.

In fact, overdosing on high-intensity exercise can actually increase the risk of death from a heart attack or stroke in people who already suffer from a pre-existing heart condition.

A new study published in the journal Heart looked at the exercise habits and survival of more than 1,000 people with stable coronary artery disease for more than a decade. Most of the participants in the study were in their 60s, and were part of a cardiac rehab program to help prevent further heart attacks or strokes.

Approximately 40 percent of the study’s participants exercised for an hour at moderate intensity two to four times a week; half of the remaining participants exercised at moderate intensity more than four times per week, and the remainder exercised less. One in ten participants admitted to rarely or never exercising.

The researchers discovered that the participants who rarely or never exercised were twice as likely to suffer a heart attack or stroke, compared to the physically active group.

More surprising was the fact that those who participated in high-intensity exercise on a daily basis were also more likely to succumb to a heart attack or stroke than people who performed more moderate exercise less often.

Although it may seem counterintuitive to suggest that exercise may play a role in aggravating heart disease, other smaller studies have also suggested the possibility.

However, the researchers conclude that the benefits of physical activity shouldn’t be questioned, but rather reinforced. The findings of this study serve to maximize the benefits of regular exercise while avoiding unwanted health issues, much like drugs and therapies.