A new beating heart preparation. Ultrastructural studies with special reference to vesiculation of intercalated discs.

An improved isolated blood perfused heart preparation was recently designed in this laboratory. The present work reports electron microscopic findings from dog myocardium kept beating in this system for 2 hr. To preserve structural integrity and to avoid artefacts, a new fixation technique was also developed. The studies show no significant differences between control and perfused myocardium. Both experimental groups present an excellent morphological preservation and, as revealed by myofibrils and bands alignment, a good symmetry of the contractile elements. The only noticeable modification is the presence of numerous vesicles in the intercalated disc. They are much more prominent in perfused than in control hearts. These vesicles are located in the undifferentiated region of the intercalated disc and contained various osmiophilic structures. The presence of similar vesicles in other areas of the cell, especially in lipofuscin granules or near disrupted granules, would suggest that the intercalated disc could be the excretory pathway of the myocardial cell. The present heart–lung preparation is therefore a valuable experimental tool for in vitro cardiac studies.