Worry about my heart-no. But I do keep an eye on general overall health. Stopped drinking and smoking decades ago. My wife makes certain we eat healthy foods. Annual physical. Probably in better health at 68 than I was at 38. I do find myself getting a bit more tired quicker when mountain biking (yeah that can happed at 68-surprise!). Don't have much comparison for how I do road riding now vs. past, as until 13 yrs ago, was strictly an off-road rider. I did have a stress test once when I drank alcohol and smoked heavily, amazing that all was OK then. It could only be better now, as life style these days is considerably healthier than past.