Pulmonary emboli are blockages in the pulmonary arteries, typically caused by blood clots that travel from the deep veins of the legs (deep vein thrombosis). They are clinically significant as they can lead to reduced blood flow to the lungs, resulting in hypoxia, chest pain, and potentially fatal complications like pulmonary hypertension or right heart failure. A common association is prolonged immobility, which increases the risk of thrombus formation.