To determine whether percutaneous transluminal coronary angioplasty (PTCA) increases coronary artery luminal dimensions by stretching and injuring ("paralyzing") the smooth muscle of the arterial wall, we prospectively analyzed spontaneous changes and then intracoronary nitroglycerin-induced changes in segmental coronary artery diameters during the first 30 minutes after uncomplicated single-vessel PTCA in 10 patients. Five additional patients received intravenous nitroglycerin throughout the procedure to determine whether nitroglycerin could prevent vasoconstriction after PTCA. All of the patients were maintained on oral doses of diltiazem and aspirin at the time of the study. Coronary arteriography was performed at 2, 5, 15, and 30 minutes after PTCA and then 3 minutes after 300 micrograms i.c. nitroglycerin. Quantitative measurements (computerized edge-detection) were performed at each time, in coronary segments centered in the dilated segment, distal to the dilated segment, and in a control vessel not manipulated with the balloon catheter or guidewire. Progressive vasoconstriction (defined as a loss of diameter that was reversed by intracoronary nitroglycerin) was observed after PTCA in the dilated and distal segments (10 of 10 patients) but not in the control segment. The vasoconstriction in the dilated segment at 30 minutes (mean, 30 +/- 4%) was highly statistically significant compared with vasoconstriction at 2 and 5 minutes after PTCA (p less than 0.001) and compared with the control segment at 30 minutes (p less than 0.005). There was no significant loss of diameter after PTCA in the dilated segment in the five patients who received intravenous nitroglycerin. In conclusion, 1) spontaneous coronary artery vasoconstriction after PTCA occurs routinely at and distal to the site of balloon dilatation despite pretreatment with aspirin and calcium channel blockers; 2) coronary artery vasoconstriction after PTCA is rapidly reversed by intracoronary nitroglycerin and can be prevented by the continuous administration of intravenous nitroglycerin during and after the procedure; 3) these results are incompatible with the hypothesis that PTCA improves coronary luminal dimensions by arterial "paralysis"; and 4) these findings have implications concerning the etiology and prophylaxis of abrupt vessel closure after PTCA.