The most common sourse of embolism -

In greater than 95% of cases, venous emboli originate from thrombi within deep leg veins proximal to the popliteal fossa; embolization from lower leg thrombi is uncommon. Depending on size, a PE can occlude the main pulmonary aery, lodge at the bifurcation of the right and left pulmonary aeries (saddle embolus), or pass into the smaller, branching aerioles . Rarely, an embolus passes through an atrial or ventricular defect and enters the systemic circulation (paradoxical embolism) ( Robbins Basic Pathology, 9 th edition, page 90 )