The purpose of this work was to show the importance of myocardial bioptate analysis using different methods in the diagram of diagnostic flow in primary cardiomyopathies in children. According to the guidelines of the Task Force on Cardiomyopathies of the WHO/ISFC, we identified 121 children (50 f and 71 m) as having cardiomyopathy, giving an average occurrence for all cardiomyopathies of 38.81 for each 10,000 pts examined in our outpatient clinics for paediatric cardiology. The dilated cardiomyopathy (DCM) was identified in 52 pts (42.9%), hypertrophic cardiomyopathy (HCM) in 43 pts (35.5%) and restrictive cardiomyopathy (RCM) in 6 pts (4.8%). We placed 11 pts (9.0%) in the group of specific cardiomyopathies. In nine pts (7.4%), it was impossible to classify the cardiomyopathy. Most of those with DCM had been diagnosed prior to the age of 3 years (RR 1.9, 95% CI 1.4-2.47). There were no statistically significant differences in the incidences of DCM as compared to HCM (Z 0.923, p < 0.1779), but we encountered a significantly lower occurrence of RCM (Z 6.044, p < 0.001). The biopsy of endocardium and myocardium was done to confirm the etiology of primary cardiomyopathy in 22 pts, 12 m and 10 f, age 1 to 17 (average age 9.5y). The bioptates were analysed by light microscope (Dallas criteria) in all pts, 13 bioptates by direct immunofluorescence, 8 by immunohystochemical method (two hystochemically by the method of coloring with Kongo red, one by the microscopy in polarised light), 7 by electron microscope, and 5 by PCR method where DNA and RNA of cardiotrophic viruses was used. Out of 10 pts with DCM, in 4 myonecrosis as a consequence of acute myocarditis and in 6 signs of late inflammatory processes, as a consequence of chronic immunologic myocarditis, were found. In 4 of them rebiopsy proved complete healing. In 5 pts with HCM the diagnosis was confirmed hystologically. One bioptate was analysed by electron microscope to rule out mitochondriopathy. Out of 4 pts with RCM due to inflammation, in 3 pathohistological findings proved diagnosis and in one showed primary amyloidosis. In one patient pathohystological finding showed fibroelastosis. In one patient heart tumor (fibroma) has been found.