EARLY experiments in open-heart surgery indicated the need for preventing air embolism from the open heart during cardiopulmonary bypass. The studies that were made by Senning1 and by Glenn and Sewell,2 independently, on deliberately induced ventricular fibrillation, were aimed at the solution of this problem, as were later studies by others on cardiac arrest induced by potassium citrate, acetylcholine, anoxia and hypothermia. Though it has been determined that the latter methods produce an ideal operative field — a heart that is completely quiet and nearly bloodless — prolonged cardiac arrest induced by any method that does not include coronary perfusion . . .