The acute haemodynamic effects of the new calcium antagonist isradipine have been studied in ten hypertensive cardiac transplant recipients. Isradipine 0.01 mg.kg-1 was given IV during right heart catheterization and noninvasively automatic blood pressure measurements. From a baseline blood pressure of 164/114 mmHg the maximum blood pressure reduction was 35 mmHg systolic, 30 mmHg diastolic, and mean 34 mmHg, due to a reduction in systemic vascular resistance, maximum 43%. Cardiac index increased 32%, mainly due to an increase in the stroke volume, as the heart rate rose only by 10%. Left ventricular filling pressure was slightly reduced. We conclude that the main effect of isradipine was a major reduction in left ventricular afterload, comparable to that previously found in other patient groups.