Ultrasound contrast agent safety has received recent attention based on reports of associated serious adverse events. The US Food and Drug Administration requested this postmarketing study of the effects of Optison on pulmonary hemodynamics. The aim of this study was to compare Optison and a placebo for effects on pulmonary artery systolic pressure (PASP) and pulmonary vascular resistance (PVR) during right-sided cardiac catheterization. This was a single-blind, crossover, placebo-controlled, multicenter study of Optison in subjects referred for clinically indicated cardiac catheterization. Based on screening echocardiographic PASP, subjects were assigned to 1 of 2 strata (1 = normal PASP [≤35 mm Hg] and 2 = elevated PASP [>35 mm Hg]), in which they were randomized to treatment arm A (intravenous 0.5 ml Optison and then intravenous 0.5 ml placebo [5% dextrose] 15 minutes later) or arm B (intravenous 0.5 ml placebo [5% dextrose] and then 0.5 ml Optison 15 minutes later). Baseline pulmonary hemodynamics were obtained within 60 minutes before the first injection and 2, 6, and 10 minutes after each injection. Thirty patients each received their assigned treatments. There were no clinically relevant increases from baseline in mean PASP or PVR (Wood units) in either stratum alone or the combined strata. There were no serious adverse events. In conclusion, there is no change in PASP or PVR after intravenous injection of Optison at a clinically relevant dose in patients with normal or elevated baseline PASP.