The QT interval is a measurement on an electrocardiogram (ECG) that represents the time it takes for the heart's electrical system to reset after each heartbeat. It starts at the beginning of the QRS complex and ends at the end of the T wave. A normal QT interval is crucial for maintaining a regular heart rhythm. Abnormalities in the QT interval can lead to serious heart conditions, such as Torsades de Pointes, a type of life-threatening arrhythmia. Factors like certain medications, electrolyte imbalances, and genetic conditions can affect the QT interval, making regular monitoring important for heart health.