The objective of this study is to investigate whether percutaneous PFO closure with the Occlutech Flex II PFO Occluder is non-inferior to the AMPLATZER™ PFO Occluder and Gore® Cardioform Septal Occluder in closure of the PFO, prevention of recurrent embolic stroke, and device/procedure related Serious Adverse Events (SAE).

Inclusion Criteria: Subjects with a PFO and cryptogenic stroke:

• PFO defined as visualization of microbubbles (during Trans Esophageal Echo (TEE)) in the left atrium within three cardiac cycles of right atrial opacification at rest and/or with Valsalva.
• Cryptogenic stroke defined as a stroke of unknown cause.
• Stroke defined as an acute focal neurological deficit, presumed to be due to focal ischemia, and either:
• Symptoms persisting ≥24 hours OR
• Symptoms persisting <24 hours with Magnetic Resonance Imaging (MRI) or Computer Tomography (CT) findings of a new, neuroanatomically relevant, cerebral infarct.

Exclusion Criteria:

• Age < 18 years
• Myocardial Infarction (MI) or unstable angina within 6 months.
• Severe mitral valve stenosis, severe aortic valve stenosis, or severe regurgitation.
• Left Ventricle Ejection Fraction (LVEF) <35%.
• Uncontrolled hypertension or diabetes mellitus despite medications.
• Subjects contraindicated for aspirin or clopidogrel.
• Presence of other comorbid conditions, or other medical, social, or psychological conditions that, in the investigator's opinion, could limit the subject's ability to participate in the clinical trial or to comply with follow up requirements, or impact the scientific soundness of the clinical trial results.
• Qualifying stroke with Modified Rankin score >3.
• Anatomy in which the device would interfere with intracardiac or vascular structures.
• Life expectancy < 2 years.
• Participation in another clinical study that can interfere with the results of this study
• Exclusion for patients with known causes of ischemic stroke:
• Atrial fibrillation/atrial flutter (chronic or intermittent).
• Left Ventricle (LV) aneurysm, intracardiac thrombus, or tumor.
• Mitral or aortic valve vegetation or prosthesis.
• Aortic arch plaques protruding >4 mm into the lumen.
• Atherosclerosis or arteriopathy of intra- or extracranial vessels with >50% diameter stenosis in the artery supplying the infarcted territory.
• Another cause of right-to-left shunting (e.g., an Atrial Septal Defect (ASD) or a fenestrated atrial septum).
• Presence of an arterial hypercoagulable state.
• Lacunar infarct probably due to intrinsic small vessel as the qualifying event, defined as an ischemic stroke in the distribution of a single, small deep penetrating vessel in a patient with any of the following:
• A history of hypertension (except in the first week post stroke).
• A history of diabetes mellitus.
• Age ≥50 years.
• MRI or CT with leukoaraiosis greater than symmetric, well-defined periventricular caps, or bands (European Task Force on Age-Related White Matter Changes rating scale score >0).
• Arterial dissection as the qualifying event.