Changes in coronary arterial size due to ergonovine maleate are described and quantitated in 90 patients - 18 with typical angina pectoris, 56 with atypical chest pain, nine with variant angina pectoris, and seven heart transplant (allograft) recipients. We observed two angiographic changes in the diameter of coronary arteries: 1) spasm, which was characterized by occlusion or marked (>85%) focal or diffuse vessel narrowing, or 2) relatively mild and diffuse vessel narrowing, which was interpreted as the normal pharmacologic response to the drug. Serial bolus injections of 0.05 mg, 0.10 mg and 0.25 mg of ergonovine maleate produced diffuse narrowing of the diameter of coronary arteries of 10 ± 1.5%, 16 ± 1.4% and 20 ± 1.3% (mean ± SEM), respectively, in the 72 patients with anginal syndromes who did not develop coronary spasm. The degree of coronary arterial narrowing was the same in heart transplant recipients and in patients with normally innervated hearts who did not develop coronary spasm. We believe the normal pharmacologic response to ergonovine maleate was due to a direct vasoconstrictor action of the drug; this action was independent of neural control extrinsic to the heart.