Summary: Coenzyme Q10 is a very important compound that performs many functions in the human body. The most important function of koeznymu Q10 is participation in the production of energy in the mitochondria, which determines the proper functioning of all cells, tissues and organs. The highest concentration of coenzyme Q10 is found in the tissue of the heart muscle. As the body ages, the concentration of coenzyme Q10 in the tissue of the heart muscle decreases, which makes it more susceptible to damage by free radicals. It has been shown that in patients with circulatory failure, the aggravation of disease symptoms is inversely related to the concentration of coenzyme Q10. Importantly, the concentration of coenzyme Q10 in patients with heart failure was an important predictor of the risk of death. Long-term coenzyme Q10 supplementation at a dose of 300 mg/day (Q-SYMBIO study) has been shown to significantly improve heart function and prognosis in patients with heart failure.