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New - portable handheld ecg ekg heart monitor,new brand
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The heart is an organ responsible for pumping the blood in the body. Through the blood, nutrients are provided to the body s cells and waste products are removed from these cells. The heart has four chambers: two upper chambers which are called atria and two lower chambers which are called ventricles. These chambers are also classified as left and right atrium and left and right ventricle, and each of them has a specific function. A schematic frontal section through the human s heart is presented in the following figure.
The heart pumps the blood by repeated contractions of its muscles. These cardiac contractions are produced due to an electrical phenomenon called depolarization, that takes place in the heart muscles cells (myocardial cells). The myocardial cells have a negative electric resting potential. Through the depolarization, this potential goes temporarily to a positive value that stimulates them to contract. Each heart cycle consists of two phases: depolarization, which represents the myocardial stimulation and repolarization, which represents the recovery phase. Both depolarization and repolarization are electrical phenomena.
Specialized conductive fibers inside the myocardium allow the transmission of cardiac stimulus to all the myocardial cells in a specific order. The atria contract first, and then the ventricles. Under normal conditions, the cardiac stimulus originates in a point, called sinoatrial node or sinus node, located in the posterior wall of the right atrium. The property of the node s cells to fire automatically and periodically an electric stimulus is called automaticity. However, the automaticity is a property posessed by all myocardial cells. In case the sinoatrial node fails to fire a stimulus, other myocardial cells will initiate this stimulation automatically.
