Nothing exemplifies human life quite so strongly as a beating heart.
Poets address it with romantic fervor and it occupies more song and movie titles than surely any other bodily organ. The heart is a miraculous muscle that, according to statistics published in World Book, does enough work in one hour to lift a weight of one and a half short tons more than one foot off the ground. As steady as a metronome during most of its lifetime, the heart nevertheless is liable to skip a beat. Advances in medical procedures help ensure that doesn't happen. It becomes necessary when coronary arteries, which supply energy to the heart by providing it with nutrients, become blocked.