The presented case report details a rare variation of a congenital heart anomaly known as double-inlet single left ventricle (DILV) – Holmes heart. Unlike other forms of DILV, the Holmes heart variant is distinguished by the absence of transposition of the great vessels. In this particular case, the diagnosis of DILV was made shortly after birth, but due to the severe nature of the condition, corrective surgery to address the defect was not performed. After a long time, the patient sought a followup examination with a cardiologist. Despite the absence of reported anginal symptoms during the visit, abnormalities were detected in the blood morphology, indicating deviations from the normal range. Specifically, the blood morphology exhibited erythrocytosis, and a high haematocrit level. Consequently, an MRI scan was recommended during the visit, which subsequently confirmed and provided a detailed description of the Holmes heart anomaly.