Embolism of material other than embolus is less common The most common material to embolize in the blood stream is thrombus, but other types of em can occur Key Facts Pulmonary embolus Usually follows thrombosis in leg veins, often deep veins in calf. Small pulmonary emboli impact in peripheral branches of pulmonary artery and cause pulmonary infarcts(often with clinical pleurisy). Large pulmonary emboli may impact in, and obstruct a major pulmonary artery, causing sudden death(massive pulmonary embolus). A small pulmonary embolus(with infarction) may be followed by a much larger, fatal embolus rpremonitary embolus? Prevention of leg vein thrombosis is the best way of preventing pulmonary embolus.