The above answers are sort of correct, but not quite. The heart pushes blood out to the body through arteries. After the exchange at the capillaries, they enter veins. Veins do have valves that always keep blood flowing back to the heart, but the heart isn’t responsible for most of the force pushing the blood back to the heart. Skeletal muscles play a huge role in moving blood back to the heart. When you flex your skeletal muscles, the veins near them squeeze the blood out into the next chamber. This keeps blood flowing back at a good rate. That’s why you should try to move your legs around during long plane flights and car rides. If you don’t, blood can stick around in one spot for a while (usually the legs) and clot. This clot can then be dislodged and can cause a heart attack or stroke. That’s where a “deep vein thrombosis” (DVT) comes from.