Correlations and dissociations between myosin isoenzymes and cardiac function

Since the observation a decade ago that several isoforms of myosin exist with differing ATPase activities, attempts have been made to correlate cardiac contractile function with myosin isoform composition. In some species, various physical and hormonal interventions have been shown to effect parallel alterations in both cardiac function and myosin isoenzyme makeup. In other species and certain experimental situations, a dissociation between cardiac function and myosin isoforms has been noted. These findings support the hypothesis that myosin isoforms play a role in determining cardiac function, but that this regulation is shared with other control systems as well. In this paper we review some of the data demonstrating a correlation and other experiments showing a dissociation between contractile function and myosin isoenzymes.