Pacerone is a medicine used to treat adults with life-threatening irregular heartbeats. Because of its serious side effects, it is used only when other treatments have not worked or are not tolerated by the patient such as if an allergic reaction takes place.

Pacerone should not be taken if someone has a very slow heart rate, a condition called  heart block which makes the heart beat too slowly, or a slow heart rate with dizzyness.

Pacerone's risks include serious vision problems, muscle problems, thyroid problems, skin problems, and digestion problems. It was revealed in 2005 by the FDA that taking Pacerone that lung and liver damage, as well as worsening heart conditions are also side effects of the drug. For this reason, Pacerone should only be taken by those adults that have life-threatening heart irregularities. Drinking grape juice is prohibited when taking this drug as it affects how the stomach will absorb Pacerone. A doctor will say whether or not the medicine should be taken with or without food.