COVID-19 pandemic is the biggest epidemiological problem of the 21st century. The severe course of SARS-CoV-2 infection in children is rare. Sometimes, especially in patients with chronic disease, COVID-19 may be insidious and life-threatening. This article presents the course of COVID-19 in a 17-year-old boy with Friedreich's ataxia-induced hypertrophic cardiomyopathy. Despite that the main symptoms of COVID-19 (i.e., fever, cough) were moderate at the beginning of the illness, the patient condition deteriorated rapidly due to cardiac problems, atrial fibrillation, and heart failure. He required antiarrhythmic treatment and pharmacological and electrical cardioversion. Moreover, because of pneumonia requiring supplemental oxygen, remdesivir and convalescent plasma therapy were utilized in this patient. For the patient recovery, the administration of the antiviral treatment was crucial.