A heart rhythm disorder that can cause fast, chaotic heartbeats.

Long QT syndrome is caused by changes in the heart's electrical system. These changes can happen due to altered DNA that's passed from parent to child. Or they can happen due to certain medicines or health conditions.

Long QT syndrome can cause a fast, irregular heartbeat, sudden fainting and seizures. In general, the heart returns to its typical rhythm. But sudden death can happen if the heart doesn't reset its own rhythm or if an external defibrillator isn't used in time to reset the rhythm.

Long QT syndrome treatment can involve lifestyle changes, medicines, a medical device, or surgery. The goals of treatment are to prevent erratic heartbeats and sudden death.