The purpose of this study was to characterize the type and prevalence of abnormalities associated with right heart catheterization. We performed detailed post-mortem examinations of 32 consecutive patients brought to autopsy with a right heart catheter in the pulmonary artery. Thrombosis (17 patients, 53 percent), hemorrhagic lesions (25 patients, 78 percent), and intimal fibrin deposition (21 patients, 66 percent) were found at sites along the entire path of the catheter. Twenty-nine patients (91 percent) had either thrombosis, hemorrhage or both. While the superior vena cava was the most common site for all lesions, seven patients had thrombosis involving the chambers and valves of the heart and four had thrombosis involving the pulmonary artery. The incidence of thrombosis was significantly higher after 36 hours of catheterization (p less than 0.05). All five patients with thromboemboli in the more proximal pulmonary arteries had catheter-related thrombosis. We conclude that there is a high prevalence of thrombotic and hemorrhagic lesions in patients dying with pulmonary catheters in place; that the risk of thrombotic complications increases with duration of catheterization; and that patients with catheter-related thrombosis are at increased risk of thromboemboli to the proximal pulmonary arteries.