Have researchers found too much running does damage to the heart?

No: Aerobic exercise will make your heart stronger and healthier improving endurance and cardiopulmonary capacity. Healthy lifestyle avoiding bad habits with healthy diet with at least 1 gr/kg of protein will help. I will advice 3 times a week weight lifting to complete a healthier lifestyle. Make it fun and enjoy your work outs. Good luck.

Grain of truth: Let's be clear: running is a very good activity for the heart and the vast majority of people who run will benefit. That said, there's a tiny increased incidence of atrial fibrillation and even of sudden death in runners but primarily because they develop symptoms and ignore them, assuming that because they run, "it can't happen to me".