Embolism, Paradoxical (EFO_1001308) is blockage of an artery due to passage of a clot (THROMBUS) from a systemic vein to a systemic artery without its passing through the lung which acts as a filter to remove blood clots from entering the arterial circulation. Paradoxical embolism occurs when there is a defect that allows a clot to cross directly from the right to the left side of the heart as in the cases of ATRIAL SEPTAL DEFECTS or open FORAMEN OVALE. Once in the arterial circulation, a clot can travel to the brain, block an artery, and cause a STROKE.