Commotio cordis (Latin, "agitation or disruption of the heart") is a rare 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 instant during the cycle of a heartbeat, 97% fatal if not treated within three minutes. This sudden rise in intracavitary pressure leads to disruption of normal heart electrical activity, followed instantly by ventricular fibrillation, complete disorganization of the heart's pumping function, and cardiac arrest. It is not caused by mechanical damage to the heart muscle or surrounding organs and is not the result of heart disease. Its incidence in the United States is fewer than 20 cases per year, often occurring in boys participating in sports, most commonly in baseball when a ball strikes a player in the chest. Commotio cordis can occur only upon impact within a narrow window of about 40 milliseconds in the cardiac electrical cycle, explaining why it is so rare. If cardiopulmonary resuscitation (CPR) combined with use of an on-site automated external defibrillator is employed within three minutes of the impact, survival from commotio cordis can be as high as 58 percent. From Wikipedia
