It will not damage your heart but make it stronger. If you take it to the extreme and attempt to run several marathons a week it may be detrimental to your long term heart health. A runners heart is usually slightly enlarged compared to a normal heart. Constantly pushing yourself to an extreme would cause the heart to enlarge even further. The heart walls also thicken. It becomes a larger more efficient pump. That is why your heart beat is only 30 to 35 bpm in the morning. You have a larger and stronger heart than the average person has and thus can pump more blood with each beat. The type of running you do can only benefit your chances of a long and disability
free life. Keep it up!! Tell you wife to do a search for "elderly runners heart" (not that you are elderly) to see examples the effects of running has on long term health.