An increase in life expectancy contributes to a steady growth of diseases of the cardiovascular system. In recent years, there has been a stable increase in the prevalence of rhythm disturbances in the population. Fibrillation and atrial flutter are among the most common causes of a decrease in the quality of life and an increase in mortality. However, the effectiveness of various methods of treatment is not absolute, and therefore the development and introduction of new antiarrhythmic drugs is particularly relevant. Thus, the use of a class III antiarrhythmic drug (niferidil) is of unconditional interest, and literature data describing the effectiveness of its use for the relief of atypical atrial flutter are extremely few. The article presents a case of successful relief of a persistent form of atypical atrial flutter in a 79-year-old patient using three consecutive intravenous injections of niferidil at a dose of 10 mcg/kg with a 15-minute interval in 19 hours after the start of therapy. The presented clinical case confirms the effectiveness of drug cardioversion with the use of niferidil and makes it possible to consider it as an alternative to electrical cardioversion in patients with atypical atrial flutter.