The direct cardiac effects of morphine, alfentanil, ketamine, etomidate, thiopentone, midazolam and propofol were measured in isolated Wistar rat hearts. Experiments were performed using a multiple conlumnar Langendorff apparatus and the hearts were perfused with a modified Tyrode solution under constant pressure. Each drug was applied from a different column in rising concentrations at 5-min intervals. Dose ranges were chosen to compare effects at sub-clinical, clinically relevant and more than clinical concentrations. Six rat hearts were chosen at random for each drug. Only thiopentone reduced contractile force at a clinically relevant concentration: measured as g contractility per g heart weight−1 (mean±standard deviation), base-line contractility was 8.8±2.4, and contractility at 10−4 mol litre−1 thiopentone was 7.1±1.5 (P<0.01). Alfentanil was the only drug to have no significant effect on the isolated heart at any concentration. Propofol was not cardiodepressant at clinically relevant concentrations, but had a lower therapeutic range than the other drugs.
