At rest, the heart usually pumps blood at a rate of 60 to 90 beats per minute. Although extra beats occasionally occur, the normal pattern (rhythm) of heartbeats is fairly regular. The heart has an electrical system that runs through the upper heart chambers (atria) and the lower heart chambers (ventricles). The electrical system controls the heart rate and rhythm. Age, diseases, and drugs can affect the electrical system and cause abnormal rhythms (arrhythmia). Some arrhythmias reduce the ability of the heart to pump blood. Some even cause cardiac arrest, a sudden and complete failure of the heart to pump blood. Torsade de pointes is an uncommon but dangerous arrhythmia that causes cardiac arrest. It disrupts the normal electrical system of the lower heart chambers (ventricular arrhythmia). During the past decade, doctors have learned that several different types of drugs can cause torsade de pointes. However, few patients with torsade de pointes due to opioids (drugs such as morphine and methadone) have been described.