Over the past ten years knowledge of the biochemistry of cardiac sarcoplasmic reticulum vesicles has been considerably extended. In almost all respects the Ca2+ pump of cardiac sarcoplasmic reticulum shows striking similarities to the Ca2+ pump of skeletal muscle sarcoplasmic reticulum. On the other hand, Ca2+ release mechanisms seem to be more complex in cardiac than in skeletal sarcoplasmic reticulum. Future research undoubtedly will involve characterizing the function of the many additional proteins present in cardiac sarcoplasmic reticulum, and determining possible roles for these proteins in regulating Ca2+ uptake and Ca2+ release by these membranes.