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#1 The heart is a two-pump organ that pumps blood to the lungs and body. The four chambers of the heart contract in a precisely timed choreography to keep the body supplied with oxygen. The two smaller chambers, called atria, push blood down to the two larger chambers, called ventricles.

#2 Blood pressure is the pressure that the blood puts on the walls of the blood vessels. It is measured in millimeters of mercury, and it depends on the force of the squeeze, the diameter and tension of the blood vessel walls, and the timing of the aortic valve closure.

#3 The heart is a muscle that conducts electricity from cell to cell. It is the only muscle in the body that can contract on its own without receiving a signal from the nervous system. The heart’s rhythm is called sinus rhythm, and it is coordinated by the SA node and the atrioventricular (AV) node.

#4 The His-Purkinje network is reliable, but it can be subject to outages. Left bundle branch block is one example: patients with LBBB have normal conduction of the portion of the impulse intended for the right ventricle through the right bundle, but conduction of the other half of the impulse is impaired; it bypasses the left bundle and must travel through the heart muscle to get to the left ventricle.

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