Aim. To conduct a clinical and pathological analysis of a case of hereditary dilated cardiomyopathy with endocardial fibroelastosis. Materials and methods. A pathological examination was conducted on a 7-month-old child. Macroscopic, microscopic, morphometric, and statistical research methods were applied. Clinical and Pathological Case. The girl was born from the third pregnancy and third physiological delivery at 38 weeks of gestation, with a birth weight of 2990 g and an Apgar score of 8–9. She was born to parents with a burdened family history — two previous male siblings had died from congenital heart disease, specifically dilated cardiomyopathy, at the ages of 6 years and 3.5 months. Ultrasound examinations of the heart during pregnancy and at 1.5 months of age revealed no abnormalities. At 7 months, the child died of acute heart failure in the context of a viral infection, at which time cardiomyopathy was diagnosed for the first time. Autopsy findings revealed dilation of the left ventricular chamber with endocardial fibroelastosis. Subendocardially, mature wavy connective tissue fibers and young connective tissue elements were found in the interstitium of the deeper myocardial layers, indicating disease progression. This led to myocardial dysfunction associated with cardiomyocyte atrophy. Conclusions. We present a case of hereditary dilated cardiomyopathy (DCMP) characterized by a combination of left ventricular (LV) dilatation and endocardial fibroelastosis, which mutually accelerated the progression of fibrotic changes in the heart and contributed to sudden death in the context of an acute respiratory viral infection. A key challenge in DCMP is determining its underlying cause—whether genetic abnormalities or immunoinflammatory mechanisms. This case, with the first manifestations of the disease at 7 months of age, highlights the critical need for early diagnosis and genetic screening, particularly in individuals with a burdened family history.