These experiments were performed as described previously (68). A 30-mm-diameter cylindrical birdcage radiofrequency coil (Bruker) with an active length of 70 mm was used, and heart rate, respiration, and temperature were monitored during imaging using a fiber-optic, MR-compatible system (Small Animal Imaging Inc., Stony Brook, NY). MRI was performed on a 7-T ClinScan system (Bruker, Ettlingen, Germany) equipped with actively shielded gradients with a full strength of 650 mT/m and a slew rate of 6666 mT m−1 ms−1. Baseline left ventricular structure and function were assessed (68). Six short-axis slices were acquired from base to apex, with slice thickness equal to 1 mm, in-plane spatial resolution of 0.2 × 0.2 mm2, and temporal resolution of 8 to 12 ms. Baseline ejection fraction, end-diastolic volume (EDV), end-systolic volume (ESV), myocardial mass, wall thickness, and wall thickening were measured from the cine images using the freely available software Segment version 2.0 R5292 ( EDV and ESV were then indexed to body mass. Mass-to-volume ratio was calculated as the ratio of myocardial mass to EDV.