RESUMEN
We report in detail ultrastructural changes and freezing damage mechanism about heart muscle and some organelles after rapid freezing. The ventricles of rat heart were cut pieces about 100-150/?m by microsiicer. The pieces were quickly injected liquid cryogen Freon 22 by Reichert-Jung spring-assistant mechanism (KF-80). The specimens frozen were rapidly transferred into substitution medium aceton and kept at -80℃(28h), then -60℃ (48h),-20℃(12h)and 4℃ (1 h). The structures of specimens frozen were well and there were no ice crystals in the area of the tissue frozen surface to 20?m depth. However, there were freezing damages in mitochondrial crista, intercellular substance and muscular fibre in the tissue surface to 30?m depth. The structure of tissue was destroyed by ice crystal over 50?m depth in the tissue. The results suggest that intercellular substance and mitochondrial crista are the most sensitive to ice crystal damage after rapid freezing of heart tissue, then the less sensitive are muscular fibre and nucleus. The unit membrane is not easy to be damaged by ice crystal.