Exercise is almost always good for your heart experts tell us. But is it possible to get too much of a good thing?

New research shows that, in fact, strenuous training — the kind many marathoners and other endurance athletes do — can indeed be harmful to our hearts, The New York Times reports.

A newly published scientific review offers reassurance as well as a reason for caution. In general, it found that while most athletes’ hearts can withstand strenuous exercise, there are exceptions. For some people — even those in seemingly good health — heavy loads of exercise might be problematic.

The upshot: It’s important to be as informed as possible about family cardiac history and potential genetic risks before starting an exercise regimen, particularly if it will be especially strenuous.

Exercise is in general extremely beneficial for heart health, according to dozens of large-scale epidemiological studies — whether a workout lasts five minutes a day or two hours a day.

But while the findings generally indicate the more people work out, the less they are at risk of cardiac problems, the benefits plateau or decline after a certain point. What’s more, studies indicate that there are seemingly healthy people for whom strenuous exercise holds unexpected dangers.

If a close family member has died unexpectedly of heart problems, you should talk to your doctor about whether you need to be tested for conditions such as atherosclerosis or cardiomyopathy, the experts say.

And we should all pay attention to symptoms such as unusual fatigue, shortness of breath or chest pain during exercise.