Aim. To study the influence of Thiotriazolin on structural and functional parameters of heart and clinical course of heart failure (HF) in patients with diabetes mellitus type 2. Material and methods. 74 patients with HF NYHA functional class II—III and diabetes mellitus type 2 were examined and divided into 2 groups. Conventional therapy supplemented by placebo and Thiotriazolin were applied in groups 1 and 2 for 30 days respectively. Clinical course of HF and structural and functional parameters of heart were estimated. Results. Improvement of LV systolic and diastolic functions, reducing HF functional class and distance augmentation in 6-minute walk test in 1 month were observed in group 2. 3-month results were the same and distance in 6-minute walk test increased additionally. In group 1 average functional class of HF in 1 and 3 months was the same. LV dimension and myocardial mass index increased and distance in 6-minute walk test decreased in 3 months. Conclusion. In patients with heart failure and diabetes mellitus Thiotriazolin as a modulator of intracellular energetic metabolism improves myocardial functional state with increase of LV systolic and diastolic functions, reduction of HF clinical symptoms. It increases exercise tolerance and prevents progressing LV dilatation.