Objective To investigate the systemic, pulmonary, and coronary artery effects of eletriptan, a new 5HT1B/1D‐agonist in patients undergoing cardiac catheterization. Methods Ten patients (two men and eight women) without significant obstructive coronary artery disease were administered 3.33 μg/kg/min intravenous eletriptan after they were given a placebo infusion of 0.9% saline solution. Serial measurements of right heart and systemic pressures were taken at 5‐minute intervals during placebo infusion, eletriptan infusion, and a 30‐minute postinfusion period. Cardiac output by the thermodilution technique and coronary angiography were performed every 15 minutes. Quantitative coronary angiography was carried out to measure coronary artery dimensions. Results A small but statistically significant increase in occluded wedge pressure (7.4 versus 8.8 mm Hg; 95% confidence interval [CI], 0.74, 2.51; P < .01), right atrial pressure (5.3 versus 6.1 mm Hg; 95% CI, 0.0, 1.4; P < .05), and mean pulmonary artery pressure (13.2 versus 14.6 mm Hg; 95% CI, 0.0, 2.7; P = .05) was observed during the eletriptan infusion compared with placebo. A statistically significant increase in systemic vascular resistance (1256 versus 1519 dyne/sec/cm−5; 95% CI, 126, 398; P < .01) and pulmonary vascular resistance (76.4 versus 100.8 dyne/sec/cm−5; 95% CI, 1.9, 46.9; P < .05) was observed in the period after drug infusion. No overall effect was observed on the coronary arteries, although a segmental right coronary artery constriction developed in one patient, possibly as a result of catheter‐induced spasm. Conclusions Eletriptan, a 5HT1B/1D‐agonist effective in migraine, causes no significant coronary artery constriction in patients without significant obstructive coronary artery disease. This finding may reflect a relative selectivity for the 5HT1D‐receptor subtype. Clinical Pharmacology & Therapeutics (1999) 66, 85–90;