"To fully understand cardiovascular diseases, it may be helpful to understand the anatomy of the cardiovascular system. It includes the following: The heart is the pump, divided into four chambers: the right and left atria and the right and left ventricles. Arteries are large vessels carrying oxygen-rich blood away from the heart and have thick, muscular walls. Arterioles are smaller arteries. Capillaries are the smallest vessels where gas exchange takes place; oxygen is delivered to tissues and carbon dioxide is carried away. Veinules are the smallest veins, which carry carbon dioxide-rich blood back to the heart. Veins are the biggest vessels that carry carbon dioxide-rich blood back to the heart and have one-way valves to prevent gravity from pulling blood backward away from the heart. The atria are the collecting chambers of the heart, located on top. The ventricles are the pumping chambers of the heart, located on the bottom. The aorta is the largest vessel, or artery, in the body; all arteries branch from it. The right side of the heart, the right atrium and right ventricle, takes CO2-rich blood and sends it to the lungs for oxygenation. The left side of the heart, the left atrium and ventricle, takes O2-rich blood and delivers it to the body. The right side is said to be responsible for pulmonary circulation; the left side is said to be responsible for systemic circulation. Because of the distances involved, pulmonary circulation is a relatively low-pressure system, while systemic circulation is a relatively high-pressure system. In fact, when we measure blood pressure we’re measuring systemic pressure."