Summary The direct pulmonary vascular effects of amrinone, a nongly-coside, noncatechole cardiotonic agent were studied in conscious newborn lambs using a double-flow probe preparation that allows separation of direct and indirect pulmonary vascular effects. Amrinone was found to be a direct pulmonary vasodilator with a threshold dose of 0.3 mg/kg. Amrinone also increased cardiac output and decreased aortic pressure at somewhat higher threshold doses (1.0 mg/kg and 3.0 mg/kg, respectively). Amrinone’s peak effect on pulmonary resistance appeared greater than its peak systemic effects. These effects were noted in both normoxia and hypoxia, and were not changed by pretreatment with propranolol.