Echocardiogram measurement
After 12 weeks of treatment, the rats in each group were weighed and anesthetized by intraperitoneal injection of pentobarbital sodium (40 mg/kg). The left ventricular (LV) long axis, left ventricular internal diameter at end-diastole (LVIDd), and left ventricular internal diameter at end-systolic (LVIDs) were averaged over 3 consecutive cardiac cycles using an Acuson Sequoia 512 ultrasound system (Siemens, Germany) with a probe frequency of 14 MHz and a depth of 3 cm at a speed of 100–200 mm/s. Left ventricular ejection fraction (LVEF) and left ventricular shortening fraction (LVFS) were also measured to evaluate the systolic function of the left ventricle [