Paradoxical embolism is an uncommon but clinically important phenomenon. Elements of diagnosis include the presence of: (1) a venous thrombus, (2) an arterial embolus, (3) a communication between the right and left heart, and (4) a thrombus traversing such a communication. Unfortunately, all of these elements can be rarely demonstrated in each case but the probability should be considered in any patient with 2 or more present. It should be suspected in patients who have evidence of systemic arterial emboli without apparent cause. A transesophageal echocardiogram with contrast should be considered in cases where paradoxical embolism is a possibility. We present a case in which a "thrombus-in-transit" was imaged across the interatrial septum in a patient with a patent foramen ovale, deep venous thrombosis, and an embolic cerebrovascular stroke.