The study included 84 children aged 12—16 years with chronic fatigue syndrome in the presence of mitral valve prolapse (MVP), who were treated with L-carnitine (Elcar 30%) and Coenzyme Q10 (Kudevita). L-carnitine is involved in metabolic processes as a carrier of long-chain fatty acids from the cytoplasm to the mitochondria to produce ATP and acetyl-CoA. Coenzyme Q10 stimulates tissue respiration (aerobic processes) and participates in electron transfer in the mitochondrial electron transport chain. The clinical efficacy of energy-rich drugs was investigated before and after their treatment. The therapy was based on the data of an investigation by M. Trivellato et al. on carnitine deficiency and on those of our trials: the children with MVP were observed to have a significant increase in malondialdehyde levels and conjugated diene oxidation indices, which underlie mitochondrial insufficiency. The investigation indicated that prior to their treatment 100% of the children had been observed to have fatigue after exercise, as well as headache, memory and attention focusing impairments, and idiopathic hypersomnia, 34% of the patients complained of palpitation, and 43% had stabbing cardialgia. Three months later, the children who had received combined energy-rich therapy were noted to have a pronounced positive effect: 82% of them had no clinical symptoms of chronic fatigue.