Fig. 2.

Group means of increasing HR-caused percent changes on τ (A) and E_ES (B). In normal (○), compared with baseline, the percent decreases in τ and increases in E_ES were significantly increased incrementally with pacing rate, indicating frequency-dependent positive inotropic and lusitropic effects. After HF (▵), increasing HR produced blunted responses with significantly smaller percent changes in τ and E_ES at each pacing rate. In contrast, concomitant LS (▴) administration with pacing caused percent decreases in τ and increases in E_ES similar to that observed before HF. Error bar indicates SE. *P < 0.05 vs. baseline; †P < 0.05 vs. before HF; ‡P < 0.05 on LS effects on HR change.