We studied whether creatine kinase appearance in venous effluent was specific for, and quantitatively proportional to, the amount of loss of functioning myocardium. Cell viability was determined by simultaneously monitoring tissue (42)K content and mechanical performance during anoxia and reoxygenation in isolated, arterially perfused, interventricular rabbit septa. The septa were paced at 42 beats/min and perfused at 1.8 ml/min per g tissue with a modified Tyrode solution at 28 degrees C. Net total creatine kinase losses of 5.3+/-2.7, 20.6+/-7.2, 55.3+/-7.6, and 110.7+/-27.1 IU/g dry wt (mean+/-SEM) were observed after 20, 30, 40, and 60 min of anoxia, respectively. Maximum (42)K losses during the same intervals of anoxia were 16.8+/-3.4, 38.3+/-2.9, 47.0+/-1.4, and 84.3+/-14.8 mmol K(+)/kg dry wt and correlated with creatine kinase losses, r = 0.97. Upon reoxygenation, (42)K content returned to a new plateau which was expressed as a percentage of decrease from control content. These unrecovered (42)K losses were -2.7+/-0.9, 0.7+/-2.9, 6.6+/-1.9, and 14.0+/-6.5% after 20, 30, 40, and 60 min of anoxia, respectively, and correlated with the creatine kinase loss, r = 0.97. Net loss of developed tension after reoxygenation was 9.0+/-2.3, 26.7+/-17.9, 31.7+/-1.1, and 60.7+/-8.8% of control after these anoxic intervals and correlated with creatine kinase loss, r = 0.92. The small enzyme loss that occurred after 20 min anoxia without evidence for irreversible loss of cell function was congruent with0.1% of total tissue enzyme content. The significant correlation of enzyme loss with the irreversible losses of potassium content and contractile performance supported the hypothesis that creatine kinase appearance in the venous effluent was the result of cell death.