Patent foramen ovale is a defect in the interatrial septum associated with cryptogenic stroke. The presumed mechanism of cryptogenic stroke due to a patent foramen ovale is the migration of thrombus from the venous side of the circulation to the left atrium with subsequent systematic embolism, called paradoxical embolization. Provacative maneuvers and pre-existing cardiopulmonary disease can cause elevation in right atrial pressure leading to right-to-left shunting through a patent foramen ovale. We report two patients with patent foramen ovale waking up with cryptogenic vascular events and found to have an obstructive sleep apnea syndrome. During nocturnal sleep, obstructive sleep apnea can cause right atrium pressure elevation resulting in right-to-left shunting through patent foramen ovale. The possibility of patent foramen ovale and an obstructive sleep apnea syndrome may be considered in patients with cryptogenic strokes-on-awakening. Further studies are needed to support our observation. (C) 2007 Elsevier B.V. All rights reserved.