The authors placed Swan-Ganz catheters in 11 preterm and 2 term infants with severe cardiopulmonary distress. The infants ranged in weight from 1100-4000 g. The procedure was performed in the neonatal ICU by jugular venous cutdown. Intracardiac pressures and oxygen saturations were measured in each chamber entered. The authors also evaluated the presence of right to left shunting through the patent ductus arteriosus and assessed the degree of pulmonary arterial hypertension. In 5 hypoxemic infants, the authors found a patent ductus arteriosus with pulmonary hypertension. Intermittent measurement of PAP served as a guide to further therapy. In 2 infants, the unexpected diagnosis of cyanotic congenital heart disease was made. The placement of flow directed pulmonary arterial catheters in critically ill infants can be performed safely at the bedside and can provide useful diagnostic and therapeutic information.