The heart is the strongest muscle in the body. Its job is to pump blood through our blood vessels by contracting in a rhythmic way. "ANF," a very powerful peptide hormone, is made by the heart. Its job is to control blood pressure and volume. It affects the part of the brain that controls body functions, as well as the kidneys, blood vessels, and adrenal glands.
First of all, I want to put an old myth to rest: your heart is not on the left side of your body. It is actually in the middle of your chest, just a little to the left, and right under your sternum. The lungs protect the heart by surrounding it and putting a sac around it called the pericardium. "Why does the strongest muscle in the body need so much protection?" is the first thing that comes to mind. It's not strong! The heart has four chambers and weighs about 300 grammes. There are two lower ventricles and two upper atria. The flow of blood from the atrium to the ventricle is controlled by valves between the two chambers.
It is a big job for the heart to pump blood all over the body. The cardiac cycle is the set of events that happen every time the heart beats. "Cardiac" comes from the Greek word for "heart." There are three main steps: atrial systole, ventricular systole, and complete cardiac diastole. After all of the blood has left the atria, the atrioventricular valves, which are between the atria and the ventricles, close to stop blood from going backward. This is the thing you would call your heartbeat. Next, the ventricles squeeze together, sending blood into the circulatory system. The ventricular systole is the name for this. Again, "pulmonary" and "aortic semilunar" valves close to stop blood from going backward. After these two steps, the heart takes a short break called complete cardiac diastole. This lets the blood fill up again and the process start over.
