Patients with cryptogenic strokes are more likely to have a patent foremen ovale than in the general population. It is speculated that these strokes are due to paradoxical embolism, that is, passage of a venous thrombus across the patent foremen ovale to enter the arterial circulation, resulting in an embolic stroke. Venous thromboembolism is rarely present in these cases of cryptogenic stroke. Thousands of patients with cryptogenic strokes have undergone transcatheter closure of their patent foremen ovale via a variety of devices. The first 3 randomized clinical trials comparing patent foremen ovale closure with medical therapy failed to show a significant advantage of patent foremen ovale closure. Three additional trials reported in 2017 had longer years of follow-up and demonstrated an advantage of patent foremen ovale closure versus medical therapy. Analysis of their data indicated that patent foremen ovale closure in patients with an atrial septal aneurysm in addition to a patent foremen ovale had a very significant decrease in cryptogenic strokes (P < .001). There was no decrease in strokes in patients without an aneurysm of the atrial septum who underwent patent foremen ovale closure (P = .37). Aneurysms of the atrial septum are easily recognized by echocardiography and are present in approximately one-third of patients with patent foremen ovales. These data suggest that closure of patent foremen ovales in patients with an atrial septal aneurysm is indicated. In patients with a patent foremen ovale without an aneurysm of the atrial septum, patent foremen ovale closure is not indicated.