Heart attack dodger here.

If you exercise, as you get older, you'll see a slow decline of performance over decades. Don't worry about that. But when you see a decline over a month, pay attention. That's often coronary arteries that are mostly blocked, blocked enough that your heart can't get enough blood under load, but not yet so blocked that you have a heart attack. When you see that, it's time for a cardiac stress test. (I mean look, if you experience crushing pain in your chest, don't ignore that either...)

Doing the above is how I wound up with two stents in my heart, without first having a heart attack. I learned from a friend's dad, who did have a heart attack.