tanventure, I'm riding three times a week and I ride about twenty miles at 13.5 MPH. Frankly, I'm just out for the exercise and not trying to ride at my max. However, I am capable of riding the same distance at about 15mph if I want to. I can easily ride 35+ miles, but my schedule and the clock just doesn't often allow it. (sorry I can't convert that info to km) Until recently I would have told you that my butt gives out after about a couple of hours and to do a four-five hour ride requres constant movement while on the saddle and as much time as possible in the drops. However.....as I just posted in another thread, I have just started using a Selle Anatomica saddle that has done away with ALL discomfort. Frankly, I think I could now ride for as many hours as my legs and lungs allow. I am overwhelmed with how good it feels. I wish I would have tried one 35 years ago...but I'm not sure they've been around that long.

Now...here's the problem. Yes, I have four stents but I also have four totally blocked and closed bypasses out of five. It's a long story but after checking with at least six doctors at some of the most prestigious hospitals in the country, no one can tell me why or what happened.
So, I am blessed by God to be alive and feeling great BUT I have a lot of truble going up large hills, even in the lowest gear. The drugs I take put a "governor" of sorts on my heart, mostly it's the Beta-blockers that do that. Here is a definition;

"Decreases the heart rate and cardiac output, which lowers blood pressure and makes the heart beat more slowly and with less force."

As you can imagine, this is exactly what you don't want when trying to ride up hills....or the mountains we have in N. Georgia.

So, my Tour De France dreams are over but I am still able to do some spirited rides, but not quite like before the heart attack. Getting old is not for the faint of heart....no pun intended. Good luck.