The heart and lungs work closely together to supply oxygen to the body and remove carbon dioxide, functioning in a continuous cycle essential for life. The process begins when the heart's right side receives oxygen-poor blood and pumps it to the lungs through the pulmonary arteries. In the lungs, the blood releases carbon dioxide and picks up fresh oxygen through tiny sacs called alveoli. This oxygen-rich blood then returns to the heart's left side via the pulmonary veins. The left side of the heart pumps the oxygenated blood out to the rest of the body through arteries, delivering oxygen to cells and tissues. After delivering oxygen, the blood returns to the heart to repeat the cycle. This pulmonary (lungs) and systemic (rest of the body) loop typically takes about 16 seconds to complete, circulating about five quarts of blood per minute. Because the heart and lungs are so interconnected, problems in one system can affect the other, such as heart failure impacting lung function or lung diseases like COPD placing stress on the heart.