Pressurized and heated carp muscles were examined by electron microscopy to clarify the effects of high pressure upon their fine structures, in relation to the changes of their physical properties. At pressures over 300 MPa, the striated structure of the myofibrils disappeared. At 500 MPa the contractile elements of the muscle fibers disintegrated, thus resulting in an appearance of irregular electron-opaque bodies. Heated muscle fibers, on the other hand, showed that the myofibrils completely lost their striations and changed into homogeneous materials. Although high pressure and heat affected the structural profiles of such cytoplasmic membrane structures as the mitochondria and endoplasmic reticulum, no membrane disruption was observed in those structures. The appearance of glycogen granules was not affected by either high pressure or heating. In addition, the texture values of carp muscles rose with an increase in pressure, and the viscoelasticity was higher in the pressurized muscles than in the heated muscles.