Ventricular fibrillation in the isolated rabbit heart.

Ventricular fibrillation has been produced in the isolated and perfused rabbit heart by stimulating electrically at a rate from 500 to 700/min. When the perfusion fluid contained normal amounts of sodium, potassium and calcium, the fibrillation persisted after the stimulation was stopped in about 40% of hearts. When the sodium was reduced to half, tonicity being maintained by sucrose or by choline chloride, persistent fibrillation was observed in 100% of hearts. The addition of eserine or of atropine or of carbachol did not alter the percentage of hearts in which fibrillation persisted. The antimalarial compounds chloroquine, mepacrine, and pyrimethamine arrested persistent fibrillation, restoring a normal rhythm.