[Show abstract][Hide abstract] ABSTRACT: Endomyocardial biopsies from patients with dilated cardiomyopathy were obtained by cardiac catheterization. Tissue samples were embedded in epoxy resin and sectioned into serial semithin sections for immunhistochemical visualization of either the apoptosis re p ressor protein or the FLICE inhibitory protein. Colocalization of apoptosis re p ressor protein and FLICE inhibitory portein was observed in cardiac myocytes, with nuclear DNA fragmentation and myofibrillary degradation. Intact myocytes were devoid of FLICE inhibitory p rotein and apoptosis re p ressor protein staining. FLICE (Fas-associated death-domain-like IL-1 - converting enzyme) inhibitory protein and apoptosis re p ressor protein were localized in the perinuclear cytoplasm, mainly in areas that showed myofibrillary degradation as visualized by fluore scence microscopy. FLICE inhibitory and apoptosis re p ressor proteins may be intracellular markers for monitoring myocardial damage in several cardiac diseases in humans.