THERE ARE CERTAIN PATIENTS ill with pericardial or myocardial disease which is etiologically undiagnosed after intensive cardiovascular examination.1-3These patients demonstrate cardiomegaly, pericardial involvement, and, usually, heart failure without adequate cause. Direct visual, palpable, and biopsy examination of the pericardium, coronary vessels, and myocardium has been useful in establishing the diagnosis in those cases of tuberculous and viral pericarditis, acute and chronic myocarditis, extensive myocardial fibrosis, lupus erythematosis, fibroelastosis, and some myocardopathies.4-7 There are current indications for pericardial biopsy: (1) chronic or recurrent pericarditis of uncertain etiology, (2) unexplained hemopericardium, and (3) possible constrictive or adhesive pericarditis. Biopsy of the ventricular myocardium may also be indicated in patients showing manifestations of myocardosis, that is, significant myocardial disease without sufficient evidence of the common causes of heart disease, such as congenital abnormality, valvular deformity, coronary arterial insufficiency, pulmonary or systemic vascular disease, or metabolic disorder sufficient to explain the