# Commotio Cordis --- **Commotio cordis** is an extremely rare (there are fewer than 10 cases a year in America) phenomenon where blow to the left side of the chest at a very specific time in the [[cardiac cycle]] results in a disruption to the cycle, initiating [[ventricular fibrillation]] or sudden cardiac arrest. It is often fatal, but swift CPR with the use of an AED can increase survival rates. It is most commonly caused by athletes being struck by small hard objects, and among those baseballs are the most common culprit. ## Cardiac Cycle Only impacts on a narrow region on the upslope of the T wave (40 ms before the peak of the T-wave peak to the peak of the T wave) will cause ventricular fibrillation, with a markedly increased likelihood with impacts from 30 to 10 ms before the peak of the T wave. ___