This study is enrolling adults between the ages of 18-60 who have a Patent Foramen Ovale (PFO). A PFO is a slit-like opening between the upper chambers (called atria) of the heart. This opening allows blood to flow between these chambers which can lead to a stroke. This study is examining an investigational device called the Encore PFO closure device. An investigational device is one that is not yet approved for commercial use by the US Food and Drug Administration (FDA) but is approved for use in this study. This study will last approximately 5 years and involve 9 visits. This is a randomized study meaning participants will be randomly assigned to receive the investigational PFO closure device or an FDA approved PFO closure device. Participants have a 50:50 chance to receive either device. Study related testing includes physical exams, blood test, echocardiogram (ultrasound test of the heart) electrocardiograms or ECG (test of the electrical activity of the heart) and the procedure to place the PFO closure device. There are risks involved with this study including access site related risks, bleeding and bruising, incomplete closure of the PFO with the closure device or other device related complications. There is potential benefit including reduced risk of a recurrent stroke.