Patients with long QT syndrome are most commonly of three types. It is important to understand several points about this potentially lethal syndrome: 1. What precipitates the syndrome? 2. What channelopathies are involved? 3. What are the characteristic T-wave abnormalities seen in patients with long QT syndrome? 4. What therapy should be initiated? 5. Who needs an ICD? Table I summarizes several key features of the different long QT syndromes.