Between October 1983 and November 1986, 20 patients suspected of having a paradoxical cerebral or retinal embolism were identified. Cerebral infarction was the most common presentation. Six patients had a patent foramen ovale demonstrated by cardiac catheterization or surgery. Three patients had a newly discovered atrial septal defect, and one had an atrial septal defect that had previously been treated surgically. Results of the cardiac physical examination, chest roentgenography, and electrocardiography were unremarkable in 12 patients. Eighteen patients had a right-to-left shunt demonstrated by contrast echocardiography. Nine of these patients underwent cardiac catheterization; seven had abnormal catheterization study results: four had a patent foramen ovale and three had an atrial septal defect. Sixteen patients received medical therapy only while four underwent surgery. All patients survived the initial insult. There were no deaths or ischemic recurrences on follow-up ranging from one month to three years. We believe that contrast echocardiography can provide important diagnostic information, even in situations in which cardiac involvement is not suspected. Additional studies are needed before the optimal treatment of presumptive paradoxical cerebral embolism can be determined.