Diltiazem is used for:

Treating supraventricular tachycardia, a rhythm disturbance of the heart. It is also used for controlling heart rate response to other rhythm disturbances, specifically, atrial fibrillation and flutter. It may also be used for other conditions as determined by your doctor.

Diltiazem is a calcium channel blocker. It works by slowing the electrical conduction in the heart, slowing heart rate, and/or normalizing heart rhythm...