how does the heart work? why can't other muscles just work

They do. Your sphincters are constantly clenched and you're always breathing.
I don't know about about the sphincters, but if Interstellar taught me anything, it's that out hearts sustain themselves on Love.

The heart has 4 chambers. The upper two chambers (atrium) and lower 2 chambers (ventricle). When the ventricles contract, the atria relax, and vice versa. Each contraction is caused by electrical depolarization. Once depolarized the chamber needs time to repolarize. there are de and repolarization phases for both the atria and ventricles catigorized by an ecg as the pqrstu waves/complexes. The heart rarely stops due to atrophy. There are usually ischemic or electricle changes that reduce the hearts output or cause lethal arthymias