Although the SA node sends electrical impulses at a certain rate, your heart rate may still change depending on physical demands, stress, or hormonal factors. The SA node is sometimes called the heart’s “natural pacemaker.” An electrical impulse from this natural pacemaker travels through the muscle fibers of the atria and ventricles, causing them to contract. This electrical signal begins in the sinoatrial (SA) node, located at the top of the right atrium. The aortic valve opens the way for oxygen-rich blood to pass from the left ventricle into the aorta, your body’s largest artery.Įlectrical impulses from your heart muscle (the myocardium) cause your heart to contract.The mitral valve lets oxygen-rich blood from your lungs pass from the left atrium into the left ventricle.The pulmonary valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to your lungs to pick up oxygen.The tricuspid valve regulates blood flow between the right atrium and right ventricle.
The Heart Valvesįour valves regulate blood flow through your heart: The left ventricle’s chamber walls are only about a half-inch thick, but they have enough force to push blood through the aortic valve and into your body. The left ventricle is the largest and strongest chamber in your heart. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. The upper chambers are called the left and right atria, and the lower chambers are called the left and right ventricles. A coating of fluid separates the two layers of membrane, letting the heart move as it beats.
The inner layer of the pericardium is attached to the heart muscle. The outer layer of the pericardium surrounds the roots of your heart’s major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body.
A double-layered membrane called the pericardium surrounds your heart like a sac. Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). In fact, each day, the average heart beats 100,000 times, pumping about 2,000 gallons (7,571 liters) of blood.
By the end of a long life, a person’s heart may have beat (expanded and contracted) more than 3.5 billion times. The heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little larger than the size of your fist.
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