Deep venous thrombosis and pulmonary embolism (DVT-PE) is a blood clot that can develop in your leg (DVT) and occasionally break off and float to the lungs (PE). Prevention is the key. In the hospital, while lying in bed, the blood flow to and from the legs is slowed down. This is because walking causes contractions of the large leg muscles which is like a secondary heart to pump this blood back to the heart. When lying down for a prolonged period (just like the increased risk of DVT while sitting in an airline seat for hours), blood flow slows and in some individuals, it can clot. There are patients who are predisposed genetically to these clots.