It has been suggested that up to 25% of the population have a previously undiagnosed patent foramen ovale (PFO), which would allow clot from the venous circulation to enter the arterial tree and cause an arterial embolus. Is PFO the real culprit ? The hypothesis is that, when a PFO is found with a peripheral arterial embolism, it increases the risk of a DVT causing an arterial embolism and that paradoxical embolus may account for a higher number of acute arterial emboli than has been recognised previously.