If you're at high risk for heart problems, doing more than an hour of intense exercise a week might not help your heart as much as doing less — it could even be less beneficial.

If you're at very high risk for heart problems, doing just 42 minutes of intense exercise a week seems to give you the best heart health boost — doing more might not help as much and could even reduce the benefits.

People who exercise a lot—like marathon runners—live longer than those who don’t, even though they don’t have fewer heart attacks. Exercise helps you live longer, but not necessarily by preventing heart attacks alone.

If you exercise hard for more than 42 minutes every day, you’re less likely to have heart problems later on.

If you swap some of your sitting time for activities like brisk walking or jogging, you might give your heart a bigger boost—especially if you're already at higher risk for heart problems.

People who exercise moderately—like jogging or cycling a few hours a week—have the lowest risk of heart attacks, but those who exercise way more than that don’t get any extra protection against heart events.