Disclosed is a method of treating chronic congestive heart failure and particularly of increasing exercise tolerance in individuals so afflicted which comprises orally administering to such individuals a therapeutically effective amount of 2-[(2,6-dichlorophenyl)amino]-2-imidazoline or a nontoxic, pharmaceutically acceptable addition salt thereof. Such oral administration is preferably in an amount of at least about 0.1 mg/day for periods of at least about one week.