In order to determine the prevalence and significance of a patent foramen ovale (PFO) in pulmonary hypertension, 58 patients were studied with transesophageal echocardiography, right-sided heart catheterization, and exercise testing. In order to examine if a PFO might be associated with a better outcome, survival was estimated, based on a formula derived from the National Institutes of Health Primary Pulmonary Hypertension Registry, for the patients with primary pulmonary hypertension (PPH). A PFO was found in 26 percent (15 of 58) of all patients studied, 25 percent (10 of 40) of those with PPH, and 28 percent (5 of 18) of those with secondary pulmonary hypertension. We found no significant difference in any hemodynamic variable or exercise tolerance between the patients with and without a PFO, or for subsets of patients with primary and secondary pulmonary hypertension. We also found no significant difference in the 1-, 2-, 3-, 4-, or 5-year estimated survival, for the patients with PPH between those with and without a PFO. The prevalence of a PFO in pulmonary hypertension appears similar to the normal population. A PFO provides no detectable influence on resting hemodynamics or exercise tolerance in patients with pulmonary hypertension and is not clearly associated with patients expected to survive longer.