Background: Moderate-to-large residual shunts following percutaneous patent foramen ovale (PFO) closure are clinically important and associated with recurrent neuro-embolic events. However, their management has not been clearly established in clinical practice. We report our experience in patients of these patients with a prior history of cryptogenic stroke and/or transient ischemic attack (TIA). Methods: All patients undergoing percutaneous PFO closure were routinely screened at six-months for residual shunts using transthoracic 2D echocardiography with antecubital administration of agitated saline contrast and color flow Doppler. Patients with evidence of moderate-to-large residual shunts were selected to undergo reintervention with shunt closure. Post-reintervention follow-up was performed at 24-hr, 30 days, and every six months thereafter. Clinical predictors of the moderate-to-large residual shunts, and the feasibility, safety and long-term efficacy of percutaneous residual shunt closure using a second device implant were examined. Results: Between 1995 and 2007, a total of 424 patients underwent PFO closure. Of these, 5% (21/424) had moderate-to-large residual shunts. Baseline characteristics among patients with moderate-to-large residual shunts and those with only none or small defects (n = 403) were similar. Multivariate analysis identified the 24-hr postprocedure shunt as the only independent predictor of residual shunting at six months. Of the 21 study patients with moderate-to-large residual shunt (mean age, 47 +/- 14), one underwent successful elective surgical repair, while the remaining 20 underwent transcatheter closure using a second device. The technique was successful in 95% (19/20), and all but one patient had complete shunt closure at six months of their percutaneous reintervention. We report no deaths, recurrent strokes or TIAs during the long-term mean follow-up period of 2.9 years. Conclusions: Our study suggests that in patients with moderate-to-large residual PFO shunts, percutaneous reintervention using a second device implant is safe and effective. (C) 2010 Wiley-Liss, Inc.