A pulmonary embolism occurs when a blood clot lodges in the pulmonary artery of the lungs, blocking blood flow. Risk factors include surgery, prolonged immobility, smoking, pregnancy, and oral contraceptive use. Symptoms range from mild to severe and include difficulty breathing, chest pain, and leg swelling. Diagnosis involves tests like chest imaging, blood gas analysis, pulmonary angiography, and lung scanning. Treatment depends on severity but may include blood thinners, clot removal procedures, or thrombolytic drugs to dissolve clots. Complications can include heart failure, recurrent clots, or bleeding from blood thinners.