I wouldn't see a doctor. I've asked three...at physical exams and once while on a ride with a doc.

Basically, it's very difficult to hurt your heart (or kill yourself) as long as it's in good shape. You have to ignore obvious signs to cause damage. That said, you should know what your maximum heart rate is, and use that in training. Do work hard on the hard days, and do recovery rides to help your body recover (i.e., Zone 1-2).

I'm 41, with a max of 192 (so far), and resting rate around 50. Today's solo century was mostly in Zone 3 at an average of 155 bpm.

Fast club rides I'll get really close to my max, and have a higher average. For instance, a couple weeks ago at a club ride my average was 167, and my max for that ride was 191. You work hard, but then you recover the next day by taking it easy.