In 93 cardiac patients the effects of low, mean and high fentanyl dosage--0.003 mg/kg, 0.015 mg/kg and 0.03 mg/kg--on haemodynamics, inotropic state and myocardial oxygen consumption were investigated during surgical procedures under basic neuroleptanalgesia. There was an increase in heart rate with the low fentanyl dosage, whereas mean and high doses lowered heart rate. Decreases in arterial pressure, left ventricular pressure, and perfusion pressure during extracorporal circulation as well are interpreted as peripheral vasodilatory effects. Most of the measured and calculated hemodynamic parameters such as PAP, dp/dtmax, CI, TSR decreased. There was, however, no decrease in myocardial contractility, when considering changes in heart rate, pre- and after-load and dp/dtmax. The decrease in heart work and myocardial oxygen consumption may be of advantage especially in patients with coronary heart disease.