Long QT syndrome is an uncommon inherited condition — meaning it's caused by genes passed on to you from your parents. The electrical activity of heart cells is controlled by a set of channels that pump minerals, such as sodium and potassium, in and out of cells. If you inherit genes that cause alterations in these channels, it can affect the action of heart cells.
Normally, an electrical impulse starts in the sinus node, located in the upper chamber of the heart. The electrical impulse then travels down to the lower chambers of the heart, called the ventricles, causing contraction of the ventricles' muscle cells. This contraction causes the blood to flow out of your heart, like how squeezing a balloon filled with water, but not tied at the top, causes the water to squirt out the top.
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