During open-heart surgery there is much to be gained from having a still heart. The danger of air embolism is minimized; blood loss is lessened, and the surgeon has a clearly visible and motionless operative field. The presumed tolerance of the still heart to ischemia might be still another important advantage. In hypothermia, operations on the ventricles would not be feasible without a method of control of the heart action.
Certain ions have long been known to have cardioplegic properties. Ringer1 discovered in 1883 that an excess of potassium is capable of stopping the heart in diastole and that an excess of calcium can do so in systole. Hooker,2 Wiggers,3 and, more recently, Swan4 have injected potassium salts into the coronary circulation in order to stop ventricular fibrillation. Inhibition of cardiac contractions by the injection of potassium chloride, acetylcholine, methacholine chloride U. S. P. (acetyl-β-methyl-choline chloride;
MERRITT DMH, SEALY WC, YOUNG WG, HARRIS JS. Potassium, Magnesium, and Neostigmine for Controlled CardioplegiaEvaluation with the Isolated Perfused Cat Heart. AMA Arch Surg. 1958;76(3):365-371. doi:10.1001/archsurg.1958.01280210035007