Commotio cordis

Commotio cordis (Latin, "agitation of the heart") is an often lethal disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart (the precordial region), at a critical time during the cycle of a heart beat causing cardiac arrest. It is a form of ventricular fibrillation (V-Fib), not mechanical damage to the heart muscle or surrounding organs, and not the result of heart disease. The fatality rate is about 65%. It can sometimes, but not always, be reversed by defibrillation.