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Figure 3 Responses of normal and stenotic coronary arteries to dynamic exercise after intracoronary phentolamine administration in patients without (; upper panel) and with chronic beta-blockade ( + ß; lower panel). For comparison purposes, data are shown also for controls (C). Coronary cross-sectional area (CSA) is expressed in percent of resting luminal area. Normal vessel size remained unchanged after phentolamine administration and increased during exercise both before and after administration of phentolamine or nitroglycerin. The CSA of the stenotic vessel segments also remained unchanged after phentolamine administration. However, in phentolamine-treated patients with or without chronic beta-blockade, paradoxical stenosis vasoconstriction was prevented during exercise. Coronary vasoconstriction was reversible after nitroglycerin administration.