Your heart pumps blood from its left side, through the aorta (the main artery leaving the heart) and into the arteries. The blood travels through your arteries, which divide off into smaller and smaller branches of blood vessels called capillaries. Travelling through this network of capillaries, blood reaches every part of your body. The de-oxygenated blood then travels back to the heart through your veins. Branches of veins join to form larger veins, which lead back to the right side of your heart. From here, your heart will pump the de-oxygenated blood to your lungs with its next heartbeat.