Not to get all metaphysical, but the heart is at the very center of who we are and what we do. It feeds the brain with nutrients and life-giving oxygen, and fuels the cells out to the extremities. Any abnormalities of the heart, especially at the controls of an airplane, can lead to stress if not calamity.
This is a companion discussion topic for the original entry at https://www.avweb.com/flight-safety/healthy-pilot-5-your-ticker-the-whole-ballgame