Although this medication and others like it are used to treat certain kinds of abnormal heartbeats, they may rarely cause serious (sometimes fatal) irregular heartbeats.

This medication is used to treat a certain serious (possibly life-threatening), persistent, abnormally fast heartbeat (sustained ventricular tachycardia).

Very low levels of potassium can lead to serious irregular heartbeats (arrhythmias).

This medication is used to treat certain types of serious (possibly fatal) irregular heartbeat (such as atrial fibrillation/flutter).

Do not take more of this drug than prescribed because you may increase your risk of side effects, including a new serious abnormal heartbeat.

QT prolongation can infrequently result in serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that need medical attention right away.

Though this medication often gives great benefits to people with irregular heartbeat, it may infrequently cause a serious new irregular heartbeat.

This medication is used to treat certain types of serious (possibly fatal) irregular heartbeat (such as persistent ventricular tachycardia).

Many heart drugs like quinidine (antiarrhythmics) are very effective, but they can infrequently cause new serious (possibly fatal) irregular heartbeats.