1
general::
1. Close behind someone, as in The dog started chasing the car but Miriam called him to heel. This expression is used almost solely in reference to dogs. The heel in this idiom, first recorded in 1810, is the person's. 2. Under control or discipline, as in By a series of surprise raids the police brought the gang members to heel. This expression alludes to controlling a dog by training it to follow at one's heels. [Late 1800s]
American Heritage Idioms