The hemodynamic effects of nitrendipine, a new calcium entry blocker, have been evaluated both experimentally and in hypertensive patients. The acute hemodynamic effects (left atrial injection of radioactive microspheres) were studied in normotensive and hypertensive (2K-1 Clip, Goldblatt) Sprague-Dawley rats; two dose levels were used intravenously: 0.3 and 3.0 mg/kg body weight. Arterial blood pressure was reduced in both groups in a dose dependent manner. Cardiac output increased with the higher dose but was reduced with the smaller dose. In humans, nitrendipine was given in a dose of 20 mg b.i.d. for 2 weeks to nine hypertensive patients. The reduction in blood pressure was due to a decrease in systemic resistance (52 +/- 9.7 (SD) to 39 +/- 5.4 u X M2, p less than 0.05); both cardiac output and heart rate response varied among patients (+ 2.1 to -0.97 L/min and + 19 to 4 bpm, respectively). Vasodilators have been previously classified according to predominance of their effects on venous or arterial system. Results of this study suggested that the same vasodilator could fall in one or the other subdivision depending on the dose used and possibly on individual responses.