Commotio cordis (CC), sudden death as a result of a blunt, often 
innocent-appearing chest wall blow, is being reported with increasing frequency. 
The clinical spectrum is diverse; however, a substantial number of cases occur 
in youth athletics. In events that occur during sport, victims are struck by 
projectiles regarded as standard implements of the game. Sudden death is 
instantaneous and victims are most often found in ventricular fibrillation (VF). 
Overall survival is poor; however, successful resuscitation can be achieved with 
early defibrillation. Autopsy is notable for the absence of any significant 
cardiac or thoracic injury. Development of an experimental model has allowed for 
substantial insights into the underlying mechanisms of sudden death. In 
anesthetized juvenile swine, induction of VF is instantaneous following chest 
wall blows occurring during a vulnerable window before the T wave peak. Crucial 
variables including the velocity of impact, impact location, and hardness of the 
impact object have been identified. Rapid left ventricular (LV) pressure rise 
following chest impact likely results in activation of ion channels via 
mechano-electric coupling. The generation of inward current via 
mechano-sensitive ion channels likely results in augmentation of repolarization 
and nonuniform myocardial activation, and is the cause of premature ventricular 
depolarizations that are triggers of VF in CC. While softer-than-standard safety 
baseballs reduce the risk of CC, commercially available chest protectors are 
ineffective in preventing CC. The development of more effective chest protectors 
and more widespread use of automated external defibrillators at youth sporting 
events are needed.