Left ventricular non-compaction cardiomyopathy is a rare genetically determined phenomenon associated with impaired myocardial compaction and the risk of developing chronic heart failure, ventricular arrhythmias, and thromboembolism. This report presents the case of a 26-year-old professional boxer, previously considered healthy, who developed edema, progressive dyspnea, and syncope after COVID-19, leading to hospitalisation. Echocardiography revealed chamber dilation, left ventricular wall hypertrabeculation, a noncompacted-to-compacted layer ratio greater than two to one, and a left ventricular ejection fraction of 21 to 28 percent. Contrast-enhanced magnetic resonance imaging confirmed left ventricular noncompaction cardiomyopathy (noncompacted myocardial mass of 23% according to the А. Jacquier et al. criterion) and signs of fibrosis. Treatment was initiated with quadruple therapy for chronic heart failure, diuretics, and rivaroxaban; no thromboembolic events were recorded. On optimal therapy, the left ventricular ejection fraction improved to 44% by November 2025, symptoms significantly regressed, and the patient returned to non-professional training. The case of detecting left ventricular non-compaction syndrome in an athlete is particularly interesting due to the complexity of differentiating between the physiological hypertrophy of an "athlete’s heart" and the excessive trabeculation and non-compaction of the left ventricular myocardium seen in left ventricle non’compaction. Intense training most likely contributed to the functional maladaptation of the left ventricle, and a prior viral infection may have served as a triggering factor in a morphologically altered heart, leading to the subsequent transition to cardiomyopathy against a background of genetic predisposition.