Your Heart and How It Pumps

Your heart is a muscular pump about the size of your fist. Its right and left sides work in series, keeping blood moving through the lungs and then through the rest of the body.

Your heart is a muscular pump in the middle of your chest, behind the breastbone and tilted slightly to the left. It contracts and relaxes continuously to move blood through the lungs and the rest of the body. The right and left sides work in series. Blood passes through one side, travels through the lungs, returns to the other side and is then pumped through the body. Four chambers and four valves The two upper chambers are the atria . They receive blood returning to the heart. The two lower chambers are the ventricles . They generate most of the pressure that pushes blood out of the heart. A muscular wall called the septum separates the right and left sides. The left ventricle has a thicker muscular wall than the right because it pumps blood through the higher pressure systemic circulation. The right ventricle pumps through the lower pressure pulmonary circulation. In a stable circulation, both ventricles still pump the same amount of blood over time. The difference is the pressure they must generate, not the long term volume they pump. The heart has four valves . The tricuspid and mitral valves lie between the atria and ventricles. The pulmonary and aortic valves sit at the exits from the ventricles. Valves do not actively pull themselves open or closed. Pressure differences across them determine when they open and close, helping keep blood moving forwards. Following blood through the heart Blood returning from the body enters the right atrium. It passes through the tricuspid valve into the right ventricle, then leaves through the pulmonary valve and pulmonary artery for the lungs. After taking up oxygen in the lungs, blood returns through the pulmonary veins to the left atrium. It passes through the mitral valve into the left ventricle, then leaves through the aortic valve and aorta for the body. The heart muscle needs its own blood supply The blood inside the heart chambers does not directly supply most of the heart muscle. The heart has its own blood vessels, called the coronary arteries , which branch from the aorta and carry oxygen rich blood into the heart muscle. The name coronary comes from the Latin corona , meaning a crown or wreath. These vessels curve around the heart like a crown, which makes the name easier to remember. After the heart muscle has used the oxygen, coronary veins carry the blood away and return it to the right side of the heart. If blood flow through a coronary artery is severely reduced or blocked, part of the heart muscle can become short of oxygen and may be damaged. How each beat moves blood forwards During ventricular filling, blood moves from the atria into the ventricles through the open tricuspid and mitral valves. As the ventricles begin to contract, pressure inside them rises. The tricuspid and mitral valves close. When ventricular pressure becomes greater than the pressure in the pulmonary artery and aorta, the pulmonary and aortic valves open and blood is ejected. As the ventricles relax, their pressure falls. The pulmonary and aortic valves close. When ventricular pressure falls below atrial pressure, the tricuspid and mitral valves can open and filling begins again. Heart sounds and murmurs The familiar first and second heart sounds are mainly associated with valve closure. The first follows closure of the mitral and tricuspid valves as the ventricles begin contracting. The second follows closure of the aortic and pulmonary valves as the ventricles relax. A murmur is an additional sound produced by turbulent blood flow. Its timing and other features can give a clinician clues about where that turbulence is occurring, but listening alone does not identify every structural or valve problem. Electrical timing comes next The chambers also need to contract in the right sequence. The next lesson explains the electrical system that starts and coordinates that timing. When the heart is affected Heart problems can contribute to chest discomfort, palpitations, breathlessness, dizziness, fatigue or swelling. These symptoms are not specific to heart disease, and later symptom lessons examine them in their own clinical context.

The heart is two pumps working in series: pressure changes fill and empty the chambers, open and close four valves, and keep blood moving forwards through the lungs and body.