A review of 101 consecutive endomyocardial biopsies taken from 90 patients over a 5 year period from 1983-1988 at HSC was performed to examine the range and sensitivity of pathological diagnoses. Patients were aged from 19 d - 19 yrs, mean 6.7 yrs, M:F = 47:43. 51 were from the right, 44 were from the left and 6 were biventricular. A definitive diagnosis could be made in 47 biopsies. 37 of these were performed only once and resulted in diagnoses of myocarditis (12), endocardial fibroelastosis (13), adriamycin toxicity (8), mitochondrial cardiomyopathy (1), Hurler syndrome (1), Type III glycogenosis (1), and Churg-Strauss syndrome (1). There was agreement with the clinical diagnosis in 34 and disagreement (with the establishment of a different diagnosis) in 3. A second biopsy was performed to monitor the progress of the disease in 7 cases (6 myocarditis, 1 adriamycin toxicity) and a third biopsy was performed in 3 patients, all of whom had myocarditis. Non-specific changes consistent with the clinical diagnosis were found in 24 biopsies (21 cardiomyopathies and 3 carnitine deficiencies). The remaining 30 biopsies had only minor non-specific changes which were non-diagnostic or normal. This study has shown that endomyocardial biopsy in children is of value in confirming or establishing diagnoses of myocarditis, endocardial fibroelastosis, adriamycin toxicity and a variety of rarer conditions. It is also of use in monitoring the course of patients with myocarditis or adriamycin toxicity. Biopsy appears less useful in the diagnosis of cardiomyopathies, in part due to the relatively non-specific pathological features of these conditions, as well as to limitations in interpretation of biopsy material. A review of 101 consecutive endomyocardial biopsies taken from 90 patients over a 5 year period from 1983-1988 at HSC was performed to examine the range and sensitivity of pathological diagnoses. Patients were aged from 19 d - 19 yrs, mean 6.7 yrs, M:F = 47:43. 51 were from the right, 44 were from the left and 6 were biventricular. A definitive diagnosis could be made in 47 biopsies. 37 of these were performed only once and resulted in diagnoses of myocarditis (12), endocardial fibroelastosis (13), adriamycin toxicity (8), mitochondrial cardiomyopathy (1), Hurler syndrome (1), Type III glycogenosis (1), and Churg-Strauss syndrome (1). There was agreement with the clinical diagnosis in 34 and disagreement (with the establishment of a different diagnosis) in 3. A second biopsy was performed to monitor the progress of the disease in 7 cases (6 myocarditis, 1 adriamycin toxicity) and a third biopsy was performed in 3 patients, all of whom had myocarditis. Non-specific changes consistent with the clinical diagnosis were found in 24 biopsies (21 cardiomyopathies and 3 carnitine deficiencies). The remaining 30 biopsies had only minor non-specific changes which were non-diagnostic or normal. This study has shown that endomyocardial biopsy in children is of value in confirming or establishing diagnoses of myocarditis, endocardial fibroelastosis, adriamycin toxicity and a variety of rarer conditions. It is also of use in monitoring the course of patients with myocarditis or adriamycin toxicity. Biopsy appears less useful in the diagnosis of cardiomyopathies, in part due to the relatively non-specific pathological features of these conditions, as well as to limitations in interpretation of biopsy material.