Q. How to control heart?

A. Heart is the seat of mind and intelligence, within which the soul is embedded. Controlling the heart means controlling the mind from all unwanted desires. The only way to control the mind is by engaging it in the service of God, someway or the other.  And the easiest way to control the mind is by chanting the holy names —

Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare
Hare Rama, Hare Rama, Rama Rama, Hare Hare