Hydroquinidine is primarily used in the medical field as an antiarrhythmic agent to treat irregular heart rhythms, such as atrial fibrillation and atrial flutter. It works by stabilizing the electrical activity of the heart, helping to restore and maintain a normal heartbeat. Additionally, it is sometimes employed in the management of certain types of tachycardia. In research, hydroquinidine serves as a reference compound in studies exploring cardiac electrophysiology and the mechanisms of arrhythmias. Its application is carefully monitored due to its potential side effects and narrow therapeutic range.