This study reports the intraoperative use of contrast and Doppler echocardiography techniques to diagnose patent foramen ovale (PFO). Fifty patients without known atrial septal defects undergoing elective cardiovascular surgery were studied. A 5-MHz esophageal echocardiographic probe was used to image the fossa ovalis (FO) and 10 ml agitated saline was injected into the right atrium during apnea. Echocardiographic contrast was then injected during end-inspiration at 20-cmH2O airway pressure. When opacification of the right atrium was complete, the airway pressure was released. During these maneuvers, color and pulsed-wave Doppler interrogation of the atrial septum were also performed. Right-to-left passage of saline contrast across the interatrial septum was seen in 11 of 50 patients (22%). Doppler echocardiography demonstrated a PFO in 2 patients without contrast evidence of shunting. Thus, the combination of contrast and Doppler echocardiography identified a 26% (13 of 50) prevalence of PFO, approximating the previously reported autopsy rate of 25%. These contrast and Doppler techniques may be useful in detecting patients at risk for paradoxical emboli and in identifying candidates for closure of the PFO.