A palpable dicrotic pulse was observed in 18 patients after open heart operation, usually after prosthetic replacement for aortic regurgitation (14 of 18 patients). Two patients had a ventricular septal defect, one had aortic stenosis, and one, mitral insufficiency. The ages of the patients ranged from 9 to 63 years, but the dicrotic pulse was more prominent and persisted longer in younger patients. The dicrotic pulse usually appeared within 48 hours of operation, persisted 1 to 60 days and was always in a brachiocephalic distribution. Determinants of the dicrotic pulse include the stroke volume, the duration of systole, the distensibility of the arterial system, the peripheral reflection coefficient, and the systemic blood pressure. Impaired cardiac function with a low cardiac output was probably the most significant factor in the occurrence of a dicrotic pulse in this series of patients.