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Figure 5 Influence of negatively inotropic agents on frequency potentiation for each of (A) metoprolol, (B) sotalol, and (C) verapamil. Time course of LV+dP/dtmax during rapid pacing before (closed circles) and after (open circles) drug injection. Results are expressed as a percent of LV+dP/dtmax observed immediately before the onset of rapid pacing. (D) The relative frequency potentiation (FP) response after drug treatment (the increase in LV+dP/dtmax after 10-s rapid pacing, observed 10 min after treatment as a ratio of the response observed previously). Both sotalol and verapamil (but not metoprolol) significantly attenuated the frequency potentiation response (analysis of variance). Abbreviations as in Figure 1.