Pulmonary embolism causes include: Blood collecting or “pooling” in a certain part of your body (usually an arm or leg). Blood usually pools after long periods of inactivity, such as after surgery or bed rest. Injury to a vein, such as from a fracture or surgery (especially in your pelvis, hip, knee or leg). Another medical condition, such as cardiovascular disease (including congestive heart failure, atrial fibrillation, heart attack or stroke). An increase or decrease in your blood’s clotting factors. Elevated clotting factors can occur with some types of cancer or in some people taking hormone replacement therapy or birth control pills. Abnormal or low clotting factors may also happen as a result of blood clotting disorders.