Contractility, Metabolism and Pharmacological Reactions of Isolated Gas-Perfused Cat Hearts

Cat hearts were perfused through the aorta with substrate-free Krebs solution for 5 min, then with 5% CO 2 -95% O 2 saturated with water vapor at 37.5°C. Heart rate decreased rapidly but contractility was maintained at pre-gas levels for 3 to 4 hours, decreasing to 25% at 10 hours. Driving the preparations at 168 beats/min did not appreciably change the time course of change in contractility. The hearts developed more tension at all resting tensions and were able to perform more work than hearts perfused with substrate-free Krebs solution, but their work capacity was less than that of hearts perfused with glucose-Krebs solution. They reacted normally to sympathomimetic amines and blocking agents. They were very sensitive to increases in perfusion pressure, developing completely reversible arrhythmias at pressures 80 to 150% above the control (60 mm Hg). Most hearts developed contractile alternans which usually was not accompanied by electrical alternation. Glycogen, lactate, pyruvate content decreased rapidly, the first to a residual level and the others to undetectable levels.