Aim: Three rare cases of histiocytoid cardiomyopathy in infancy are reported. Patients: arrhythmias first occurred in a month after girl J.’s birth. Myocarditis, 2 atrial septal defects (ASD), and left ventricular noncompaction cardiomyopathy (LVNC) were diagnosed when she was 6 month old. The girl died at the age of 8 months. Girl V. with dilated cardiomyopathy died suddenly and unexpectedly at the age of 22 months. The boy who was diagnosed with enterovirus myocarditis and who suffered from ventricular arrhythmias died at the age of 12 months. Results: two ASDs and LVNC were confirmed in girl J. at autopsy. The autopsy performed on girl V. revealed fibroelastosis of left chambers and subendocardial yellowish plaques of both ventricles and in the mitral valve. The autopsy on the boy revealed fibroelastosis of left atrium. Histological examination revealed myofiber disarray in the interventricular septum (IS) and in both ventricles in all three cases. Some focal islands of Purkinje-like cells were found near the endocardium of both atria, in the IS, near the bundle of His and the atrioventricular node. In the atria, along with these cells, there were also T-like cells of the cardiac conduction system (CCS). The girl V. had Purkinje-like cells in the mitral valve. Immunohistochemistry showed positive staining of the cells for HCN4, myosin heavy chain, and desmin. Two infants had active myocarditis. Conclusions: Histiocytoid cardiomyopathy could be diagnosed only histologically and was proven immunohistochemically using HCN4 as a cell marker for the CCS.