Blunt precordial blows triggering ventricular fibrillation (commotio cordis) represent a leading cause of sudden death in young athletes. Attention has focused on the primary prevention of these tragedies with chest barriers. The U.S. Commotio Cordis Registry was accessed to determine the likelihood of sudden death in athletes exposed to precordial blows while wearing chest protectors. Of 182 cases of commotio cordis, 85 (47%) occurred during practice or competition in organized sports. In 32 of these 85 competitive athletes (38%), fatal chest blows occurred despite the presence of potentially protective equipment. Athletes wore standard, commercially available chest barriers made of polymer foam covered by fabric or hard shells, generally perceived as protective from arrhythmic consequences of the blows. These events occurred in 4 sports: hockey (n = 13; 1 goalie), football (n = 10), lacrosse (n = 6; 3 goalies), and baseball (n = 3; all catchers). Scenarios included the failure of the padding to cover the precordium so that blows circumvented the protective barrier (n = 25) or projectiles that struck the chest barrier directly (n = 7). In conclusion, a significant proportion (about 40%) of sudden deaths reported in young competitive athletes due to blunt chest blows (commotio cordis) occur despite the presence of commercially available sports equipment generally perceived as protective.