“…Several studies have been carried out on the effects of anoxia, substrate depletion, or metabolic inhibitors on cardiac muscle (Trautwein and Dudel, 1956;Webb and Hollander, 1956;Kleinfield et al, 1961Kleinfield et al, , 1962de Mello, 1959;Boulpaep, 1959;Lullmann, 1959). In both atrial and ventricular muscle the earliest effects were depression in force of contraction and reduc-tion in action potential duration.…”