Spontaneous alterations in coronary blood flow velocity before and after coronary angioplasty in patients with severe angina. Cyclic coronary artery flow variations with a spontaneous decline in coronary blood flow to very low levels have been documented in stenosed canine coronary arteries with endothelial injury. These flow variations are associated with transient platelet aggregation and dislodgment and the release of selected mediators, including thromboxane A2 and serotonin. However, cyclic or spontaneous flow variations have not been demonstrated in stenosed coronary arteries in humans. In this study, the hypothesis was tested that spontaneous coronary blood flow velocity variations occur in some patients with stenosed coronary arteries before or after coronary artery angioplasty. Thus, 13 patients with severe and limiting angina underwent intracoronary pulsed Doppler velocimetry of their dilated artery immediately before and after percutaneous transluminal coronary angioplasty, whereas 9 control patients underwent velocimetry of an angiographically normal coronary artery. A 3F catheter with a 20 MHz Doppler crystal was positioned to achieve a maximal stable signal, and the flow velocity signal was recorded continuously for 20 min. Spontaneous flow velocity variations (greater than or equal to 38% change in Doppler frequency shift with wide morphologic changes) were present in 3 of the 13 patients tested. Spontaneous flow velocity variations occurred before angioplasty in one patient, after angioplasty in another and both before and after angioplasty in a third. In addition, 2 of the 13 patients, 1 with spontaneous coronary artery flow velocity variations before angioplasty, had frank vasospasm in an adjacent area just distal to the area of coronary dilation immediately after balloon inflation. These data establish that spontaneous coronary artery flow velocity variations occur in some patients with severe and limiting angina before and after coronary angioplasty. These variations may be related to platelet aggregation or coronary vasoconstriction, or both, at sites of endothelial injury resulting from plaque fissuring or ulceration and endothelial and medial injury occurring during coronary angioplasty. 