Condition resulting from a sharp non-penetrating blow to the chest, probably during an electrically vulnerable phase of the cardiac cycle. The blow disrupts the heart beat, resulting in an irregularity, such as ventricular fibrillation, which may lead to a potentially instantaneous and lethal cardiac arrest. Although cardiac concussion is regarded as rare by some cardiologists, others claim that it represents one of the most common mechanisms of sudden death in young athletes. It has been most commonly reported after blows with projectiles such as baseballs, softballs, or hockey pucks. See also cardiac contusion.