Comparative Effects of Morphine and Fentanyl on Isolated Heart Muscle

Although a direct myocardial depressant effect of morphine would also be predicted as a theoretic possibility, there has been no consensus in the literature on this matter. In isolated heart preparations, morphine produced transitory stimulation followed by depression.'v637 Minor increases and decreases of cat papillary-muscle isometric tension have also been reported.8 In dogs maintained on total cardiac bypass, morphine increased right ventricular contractile force.9 In other dogs prepared with a right heart bypass, morphine elevated the left ventricular function curve and the rate of rise of ventricular pressure.9 However, morphine has also been shown to decrease the rate of rise of canine left ventricular pressure; since proportional changes also occurred in the end-diastolic pressure, no alteration in myocardial contractility was thought to have occurred.10 On the basis of ballistocardiographic observations, morphine appeared to be free of any effects on myocardial contractility in man.11