Estimation of fibrosis in endomyocardial biopsy specimens (EMB) is integral to their assessment; typically, EMB fibrosis is assessed qualitatively. We quantitated percent fibrosis in 697 paraffin-embedded, Masson's trichrome stained EMB taken from 6 sites along the right ventricular septum and from 1 site in the left ventricular free wall, utilizing Caves-Schultz (C-S) and Cordis (C) bioptomes and a scalpel in 34 formaldehyde-fixed autopsy hearts, 22 of which were anatomically normal (AN) and 7 of which were idiopathically dilated. Total tissue area and area of fibrosis were quantitated by computer-based image analysis. The mean total areas as obtained by the C-S and C bioptomes and scalpel were 0.0535 cm2 (+/- 0.028), 0.0338 cm2 (+/- 0.020), and 0.4370 cm2 (+/- 0.144), respectively. The C-S and C bioptomes and the scalpel from all hearts yielded percent fibrosis of 10.6, 12.3, and 5.4, respectively. The AN hearts had percents of 9.3, 11.8, and 4.5, while the ID hearts had 11.0, 13.7, and 7.3% fibrosis, respectively, by each sampling method. A consistent pattern was observed: the larger the piece of endomyocardium, i.e., scalpel greater than CS greater than C, the lesser the quantitated percent fibrosis. Thus, beyond allowing for biological variability in the degree of endomyocardial fibrosis, the impact of EMB size and the biotome type must be accommodated in qualitative surgical reports pertaining to myopathic hearts.