The heart has four chambers and uses valves to ensure blood flows in one direction. The right side receives deoxygenated blood and pumps it to the lungs, while the left side receives oxygenated blood and pumps it to the body. Arteries carry oxygenated blood away from the heart while veins carry deoxygenated blood back to the heart. Capillaries are the smallest blood vessels that allow for the exchange of oxygen, nutrients and waste. Plasma contains nutrients and waste while red blood cells carry oxygen and white blood cells help fight infection. A healthy lifestyle including exercise and a low-fat diet can help keep the heart strong.