PFO and ASA have been associated with stroke in many, but not In the Patent Foramen Ovale in Cryptogenic Stroke Study (PICSS), a PFO was detected by transesopha- geal echocardiography more often in patients with crypto- genic stroke than in those with known causes of stroke (39.2% Another study also found that the prevalence of PFO was greater among patients with cryp- togenic stroke than among those with known causes of stroke, including patients <55 years of age (OR, 4.70; 95% CI, 1.89 A meta-analysis of case-control studies of patients who have had an ischemic stroke found that among patients 55 years of age there are significant associations with PFO (OR, 3.10; 95% CI, 2.29 4.21), ASA (OR, 6.14; 95% CI, 2.47 15.22), and PFO plus ASA (OR, 15.59; 95% In patients >55 years of age, the associa- tion with PFO was not significant (OR, 1.27; 95% CI, 0.80 2.01), although it was for ASA (OR, 3.43; 95% CI, 1.89 6.22) and for PFO plus ASA (OR, 5.09; 95% CI, 1.25 20.74). In a population-based study from Olmstead County, Minnesota, in which the mean participant age was 66.9 13.3 years, PFO was not associated with increased risk of stroke (HR, 1.46; 95% CI, 0.74 2.88), whereas there was an association with In the multiethnic NOMAS, in which the mean age was 68.7 10.0 years, PFO was not associated with increased risk of stroke (HR, 1.64; 95% CI, 0.87 3.09), nor was the coexistence of PFO and ASA Another study examining the characteristics of PFO observed larger PFOs, longer tunnels, and a greater frequency of ASA in patients with stroke than in those without stroke.490 One study of patients with cryptogenic stroke found that the risk of recurrent stroke was 2.3% (95% CI, 0.3 4.3) among patients with PFO alone, 0% in those with ASA alone, 15.2% (95% CI, 1.8 28.6) in patients with both PFO and ASA, and 4.2% (95% CI, 1.8 6.6) in patients with Further analyses from NOMAS with longer follow- up also failed to find evidence for an increased risk of first stroke with PFO (adjusted HR, 1.10; 95% CI, 0.64 1.91) and provided further evidence that PFO is not associated with sub- clinical cerebrovascular disease.492 No study has examined treatments to prevent initial strokes in patients with PFO or ASA. 