Interesting peripheral anecdote from my experience...
I come from a line of hypertension, cholesterol, and heart-disease-related issues. Men in my family tend to die well under average life expectancy, nearly always from stroke or congestive heart failure or similar events. Knowing this, I exercise regularly and extensively, keep to a strict (vegetarian) diet, and have my cholesterol levels checked regularly. I focus on endurance sports in my training and recreation, including triathlons. I am a few years shy of forty years old. (I can't believe it, even having just put it down there. :P )
My resting heart rate is seldom under 75, and when I'm "cruising" at a comfortable pace for distance (running or cycling) it's usually 175 to 180. When I'm in interval training or pushing for speed, my heart rate exceeds 190, and during the final stretch in any race (when I'm going all out) I'll exceed 200 and hold it for 5-10 minutes. Upon starting cool-down, it drops rapidly - usually to 160 or less within one minute. At no point am I in distress - no chest pains, no dizziness or light-headed feeling, no nausea, etc.
Reviewing it with my doctor, and even having EKG run, shows that I apparently just have a fast-beating heart. Healthy, sound, and clear, but fast nonetheless. Makes all the charts on the exercise equipment and on the wall at the gym fairly useless for me.