In 16 adult patients, IV ketamine, 2.2 mg/kg body weight, did not produce dramatic effects on left heart function or systemic circulation. Minute O2 consumption and O2 delivery were stable. An appreciable elevation in pulmonary vascular resistance occurred which secondarily increased right heart work. Total intrapulmonary shunt initially increased; however, the effect was short lived and did not cause clinical alterations in PaO2. The authors conclude that physiologic alterations associated with ketamine are more pronounced on the pulmonary than on the systemic vascular bed, and to the right rather than to the left side of the heart.