[Myocardial ultrastructure of rats exposed aboard biosatellite "Cosmos-936"].

Hearts of rats flown for 19.5 days aboard the biosatellite. Cosmos-936 and decapitated 4.5--9 hours or 25 days postflight were examined electron microscopically. Hearts of weightless rats sacrificed at R + O showed marked and consistent changes in capillaries and venules; myelin transformation of membranes of mitochondria and sarcoplasmatic reticulum was seen in cardiomyocytes which did not show lysis. It is assumed that development of myelin bodies and increase in the number of autophagosomes in weightless rats were caused by disintegration of mitochondrial and sarcoplasmatic reticulum structures. Rats exposed inflight to artificial gravity displayed less pronounced submicroscopic changes.