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Long Q-T syndrome 5 (LQT5) is a rare disorder of the heart’s electrical system that can be congenital (present at birth) or acquired. In long Q-T syndrome 5, there is a defect in ion channels in the cells of the heart, causing a delay in how long it takes for the heart’s electrical system to recharge after each heartbeat. The Q-T interval on an electrocardiogram (ECG) represents the time it takes for the heart’s electrical system to fire an impulse through the heart’s ventricles and then recharge; in other words, how long it takes for the heart muscle to contract and then recover. In long Q-T syndrome 5, the 5 refers to the type of ion channel that is affected.