When is bradycardia useful for the body?

Angina pectoris: Most coronary blood flow occurs during diastole (when the heart is at rest). For patients with blocked arteries and chest pain, slowing the heart rate prolongs diastole allowing more time for blood to get to the heart. Beta blockers are used to slow the heart rate and are effective in controlling chest pain.

Slow heart rate: A healthy heart closely regulates its rate to provide the amount of blood that it needed. Seasoned athletes often have resting bradycardia because their stroke volume (amt of blood pumped per beat) is large and their peripheral muscles are efficient. People with angina benefit from bradycardia because it reduces their myocardial oxygen consumption. Pts with mitral stenosis also benefit.