Abstract
Further observations have been made on ventricular fibrillation induced by electrical stimulation in the isolated rabbit heart, in extension of the finding that fibrillation was arrested by cooling from 37 degrees to 32 degrees . The observations now made suggest that at 37 degrees the isolated rabbit heart perfused with Locke solution is on the edge of anoxia, but that at 32 degrees the oxygen supply is adequate. At the lower temperature the proportion of hearts fibrillating at any given potassium concentration was reduced, so, although the proportion of hearts fibrillating rose as the potassium concentration fell, even when the latter was one-quarter of the normal the proportion was not higher than 67%. The relation of the concentration of calcium ions to the proportion of hearts fibrillating changed from biphasic at 37 degrees to almost rectilinear at 32 degrees , the proportion increasing as the concentration of calcium ions rose. It was confirmed that a reduction in sodium concentration also raises the proportion of hearts fibrillating.