Fig. 7. The relation between the contractile force of isometric myocardial trabeculae (expressed as percent of baseline value) and stimulation rate (expressed in Hz). In trabeculae from control swine, increased stimulation frequency initially augments contractile force (a positive force–frequency relation). In contrast, trabeculae obtained after lobectomy exhibit a decline in contractile force with increasing stimulation frequency (a negative force–frequency relation). Trabeculae were not obtained from sham animals. * Difference relative to control.