Spontaneous Microscopic Activity in Cardiac Muscle

Abstract

WHEN the heart stops beating, pulsations in individual cardiac muscle fibres continue. This can be observed by examining thin sections of living cardiac muscle under high-power magnification and transmitted light. The pulsations appear to be due to alternate relaxations and contractions of the fibres, with a concomitant change in the width of the striations. Under low-power magnification and by reflected light, the activity seen in the isolated mammalian heart is that of spontaneous minute contraction waves. Prinzmetal et al.¹ have noticed a similar though much faster activity in human and dog fibrillating auricles. It disappeared with the cessation of fibrillation.