A) Representative m-mode images from WT (left) and KO (right) mice. Bar graphs depict cumulative echocardiographic measurements obtained in conscious male mice 27-30 months old, with heart rates between 650-750 beats per minute (p=ns between WT and KO) [WT, KO; n=8,7]. B) Fractional shortening, C) LV Diameter, D) LV Wall thickness. Abbreviations used: LV, left ventricle; LVDd, LV end-diastolic dimension: LVDs, LV end-systolic dimension; IVSd, intraventricular septum end-diastolic dimension; LVPWd, LV posterior wall end-diastolic dimension; IVSs, intraventricular septum end-systolic dimension; LVPWs, LV posterior wall end-systolic dimension. Data are presented as mean±SEM. *p<0.01.