The occurrence of inclusions within membrane-limited structures that run longitudinally in the cells of mammalian heart muscle.
D000818:Animals; D002415:Cats; D002462:Cell Membrane; D003594:Cytoplasmic Granules; D006329:Heart Conduction System / Q000166:cytology*; D006352:Heart Ventricles / Q000166:cytology; D008854:Microscopy, Electron; D010210:Papillary Muscles / Q000166:cytology*