Factors related to the initiation of ventricular fibrillation in the isolated heart; effect of calcium and potassium.

Ventricular fibrillation can be initiated in the isolated, perfused heart by injections of calcium chloride into the perfusion stream. It can also be initiated by perfusion with a K-free perfusion medium. These are related phenomena since the latter type of fibrillation will not occur if Ca is also removed from the perfusion medium. The mechanism by which Ca initiates fibrillation is unknown. The facility with which Ca causes fibrillation is increased when the K concentration of the tissue fluid is lowered. When it is very low the normal Ca content of Krebs solution is sufficient to initiate fibrillation.