The aim of this study was to assess (1) the incidence of patent foramen ovale (PFO) in carcinoid syndrome (CS) and (2) the feasibility of percutaneous closure procedure in selected patients with CS. One hundred eight patients were prospectively studied: 54 with CS and an age- and gender-matched control group. All patients underwent conventional and contrast echocardiography. Patients with clinical signs of dyspnea (New York Heart Association class > or =III), cyanosis, carcinoid heart disease (CHD), and severe PFO were referred for the percutaneous closure of PFO. The prevalence of PFO was 41% in patients with CS and 22% in the control group (p = 0.03) and was significantly higher in patients with CHD (59%, p = 0.009). Four patients (14% of those with CHD) were referred for the percutaneous closure of PFO, and 3 patients ultimately underwent PFO closure (using Amplatzer septal occluders). At 6-month follow-up, New York Heart Association class was improved in all patients, as well as arterial blood gas results (p = 0.04) and 6-minute walking distance (p = 0.03), but all patients presented residual right-to-left shunts. In conclusion, this prospective study demonstrates that in patients with CHD, the prevalence of PFO is high and that percutaneous closure of PFO is feasible, with a reduction in symptoms but with residual shunting.