In 29 consecutive patients (pts) coronary wedge pressure (CWP) was determined as an indicator of coronary collateral function during coronary angioplasty. Collaterals to the target vessel were angiographically detectable in 21 pts. CPW, aortic pressure (AOP), pulmonary wedge pressure (PCP), intervals to appearance of angina pectoris, surface and intracoronary ECG-changes were registered during two (n = 10) or three (n = 19) consecutive balloon dilatations. A total of 21 pts received 0.8-1.0 mg nifedipine intravenously before a second or third dilatation was performed; a control group (n = 8) received placebo. Hemodynamic parameters were reproducible for all dilatations without nifedipine. After administration of nifedipine significant changes occurred: decreases of CPW (from 34 to 29 mm Hg), AOP (from 121 to 110 mmHg), and PCP (from 12.4 to 9.4 mm Hg), and increase of ischemic tolerance time (angina pectoris) (from 35 to 56 s) (p less than 0.01). Changes in CWP and AOP showed a statistical tendency to correlate (p = 10). Thus, intravenous administration of nifedipine can improve ischemic tolerance during coronary angioplasty. Simultaneous measurement of coronary wedge pressure could not prove enhancement of collateral function as being responsible for these antiischemic effects.