Giant mitochondria in a cardiomyopathic heart.

Giant mitochondria (megamitochondria) measuring up to 14 microm in length and 3 microm in width are sporadically present in an exclusively interfibrillar position in the cardiomyocytes of a patient with restrictive cardiomyopathy. The number of cristae is augmented in the megamitochondria; these internal membranes are for the most part irregularly arrayed, but in certain giant mitochondria they run a parallel, zigzag course imparting a paracrystalline appearance to such organelles. Many of the giant mitochondria have one or several lucent, single membrane-bound inclusions that contain either alpha- or beta-glycogen particles. Megamitochondria probably originate at least in part by fusion of adjacent organelles.