A paradoxical embolus is a blood clot that originates in the venous circulation, but actually ends up on the arterial side. It may cause a stroke or some other arterial side vascular infarct. How? You know it can't squeeze through the pulmonary circulation and come squirting out the aortic valve. Therefore it must have a direct path from the vena cave into the left side of the heart. And in a reasonable number of people one exists. Specifically an atrial septal defect. In this scenario, the embolus comes into the right atrium, but shoots through the atrial septal defect into the left and atrium and then out aortic outflow tract. Did you figure it out?
 

Mark Braun, MD braunm@indiana.edu
Copyright 1998, the Trustees of Indiana University