The direct cardiac effects of ketamine studied on the intact isolated rabbit heart.

The effects of ketamine on the inotropic and chronotropic responsiveness of heart were examined in spontaneously beating hearts isolated from rabbits by using a modified Langendorff preparation. The changes of maximum left ventricular dP/dt from baseline level after exposing to ketamine 5, 25 and 125 micrograms/ml averaged +7.1% (P < 0.05), +2.8% (P > 0.05) and -42.6% (p < 0.001), respectively. The decreases of heart rate at the three ketamine concentrations averaged 2.4% (P < 0.05), 9.4% (P < 0.01) and 36.8% (P < 0.001), separately. Our data demonstrate that ketamine has dual actions on the cardiac inotropism. It mildly increases cardiac contractility at low concentration whereas at high concentration it depresses myocardium profoundly. Besides, ketamine produces a dose-dependent inhibition on chronotropism directly.