A medical illustration showing the anterior view of the circulatory system and cross-sectional view of a vein with deep vein thrombosis (DVT). DVT occurs when a thrombus (clot) forms in a deep vein of the leg which can lead to emboli breaking off from the thrombus and traveling to the heart. Anatomy highlighted in this view includes the heart, inferior vena cava (IVC), and the popliteal vein.