Pulmonary embolism is a blockage in one of the pulmonary arteries in the lungs. It can be life-threatening and cause symptoms like shortness of breath, chest pain, and coughing up blood. The document discusses the pathophysiology, risk factors, clinical presentation, diagnostic workup and imaging for pulmonary embolism. It notes that imaging tests like CT scans, ultrasound of the heart and lungs, and ventilation-perfusion scans are used to diagnose pulmonary embolism, and that electrocardiograms and blood tests are also part of the evaluation. Assessment tools like the PESI score are used to determine the severity and risk.