How is low hear rate linked to longetivity?

Excellent question: The link is probably multi-factorial, in my opinion. Disease-related low heart rates excluded, a lower heart rate is usually associated with good fitness & lower levels of stress related hormones. Some cite a genetic limit on number of heart beats that a heart is capable of, which would mean the slower the rate, the longer it will beat. There are many factors: some causal; some just associated

Less is more: Any of you who take up regular aerobic exercise will notice that your resting pulse rate will drop over time -- meaning that your heart does not have to work as hard and beat as many times per minute to get nutrients and oxygen distributed to all of your body. It is difficult to test the hypothesis that there are a specific number of beats in a lifetim.e