Previous studies have shown myocardial depression to occur secondary to toxic extracts of burned mouse and human skin and secondary to toxins present in acute human burn serum. The present report describes myocardial depression in an arterially perfused rabbit interventricular septum as a result of toxins present in acute burn plasma.New Zealand white rabbits subjected to a 25% BSA full-thickness burn were heparinized and exsanguinated 2 hours postinjury. Cellular elements and plasma were separated and the plasma frozen.Rabbit myocardial septa were then perfused with normal or burn plasma. Rabbit red cells were added to restore hematocrit to 20°, and the plasma-red cell mixtures were equilibrated with 98% O2+ 2% CO2. Temperature (28°C), pH (7.40), and flow rate (1 ml/min) were constant for all trials.All normal plasma preparations showed an improvement in developed tension (DT) during the 30-60 minute perfusion period with mean % change = + 10.5. A corresponding increase in dP/dt was also noted for all normals (mean % change = + 14.3); all septa perfused with acute burn plasma showed a decline in myocardial performance during a similar perfusion period. Mean % change in DT for burn plasma preparations was − 57.5, and in dP/dt for these septa was − 59.5.Significant myocardial depression occurs in arterially perfused rabbit septa when acute burn shock plasma is used as the perfusate.