Fig. 1. (  A ) Representative trace demonstrating the effect of α^1a-adrenoreceptor activation with phenylephrine (PE) on myocyte shortening and intracellular free Ca²⁺concentration in a single ventricular myocyte. (  B ) Summarized data for the effects of phenylephrine on myocyte shortening and intracellular free Ca²⁺concentration. Results are expressed as percent of baseline. Values represent mean ± SD in this and all subsequent figures. Control (Ctrl) represents the steady state baseline value for twitch amplitude or the change in intracellular free Ca²⁺concentration, set to 100%. *  P < 0.05 compared with control. n = 18 cells from 7 hearts.