In modern veterinary medicine, the simultaneous occurrence of chronic heart failure and chronic kidney disease is often found. However, the cause and effect often exchange places, which creates great difficulties in the animals’ treatment. Chlofusan acts on both systems. It improves cardiac and renal functions by means of providing cardioprotective and nephroprotective effects. Models of chronic heart failure and chronic kidney disease in rats provide important information on the pathophysiology of these diseases in other animal species, and the assessment of changes in the biochemical analysis of blood makes it possible to assess the state of the heart and kidneys in the study. In the course of research, the results of rat biochemical analysis were studied on models of chronic heart and kidney failure with the introduction of an exogenous nitric oxide donor. Chlofuzan contributes to a partial balance restoration of biochemical blood parameters in rats, which indicates the restoration of the mutual work of the heart and kidneys.