Heartbeats (How the Heart Works)
Your heart is a hollow muscular organ that pumps blood around your body. This is necessary for life because the blood carries the oxygen we breathe and the food we eat to all the cells of the body. The blood also carries the waste products away from the cells.
Humans have a heart with four chambers. A heartbeat is a two-part pumping action that takes about a second. Blood collects in the two upper chambers of the heart (the right and left atria). When these chambers are full, a group of specialized cells (the sinoatrial node) sends out an electrical signal that makes the atria squeeze (contract). This contraction completes the filling of the resting lower heart chambers (the right and left ventricles) by pushing a little extra blood through the mitral and tricuspid valves.
The ventricles are the muscular chambers of the heart. The right ventricle pushes blood through the lungs. Because the left ventricle pumps blood to the rest of the body, it is more muscular. The period when the ventricles are filling is called diastole. The bottom number in your blood pressure is measured at this time. When the ventricles are contracting, it is called systole. Systole is the top number in your blood pressure.
Once the bottom muscular chambers of the heart are full of blood, slightly delayed electrical signals from the atria travel along a network of cells to the ventricles, causing them to contract. As the tricuspid and mitral valves shut tight to prevent a backflow of blood, the pulmonary (pulmonic) and aortic valves are pushed open. While the right ventricle pushes blood through the lungs to pick up oxygen, oxygen-rich blood flows from the left ventricle to the heart and other parts of the body.
When the ventricles relax, the pulmonary and aortic valves close. The lower pressure in the ventricles causes the tricuspid and mitral valves to open, and blood stored in the atria rushes in and the cycle begins again.
Your heart beats faster and works harder during times of exertion. It works less hard and beats more slowly when you are resting. Your brain sends signals to the heart to meet the needs of your body. By avoiding smoking and controlling blood pressure, cholesterol, and blood sugar, you may help your heart stay healthy longer.