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II. Echocardiography studies Mice were anesthetized with Halothane (0.75 – 1.25%, 1 l/min). Images were obtained with the transducer placed on the animal’s shaved chest (lateral recumbance). To optimize the image, a transmission gel was used between the transducer and the animal chest (General Imaging Gel, ATL. Reedsville, USA). Animals were scanned from below through a hole in the surgical bed, at 2-cm depth with the focus optimized at 1-cm. All measurements were based on the average of three consecutive cardiac cycles. Two-dimensional (2-D) images of the heart were first obtained in the parasternal long-axis view, followed by short-axis and apical 4-chamber views. Left ventricular end-systolic (LVESD) and enddiastolic dimensions (LVEDD), interventricular septal thickness (IVST), and posterior wall thickness (PWT), both in diastole and systole, were measured at the level of the papillary muscles on the short-axis view using 2-D guided M-mode imaging. The angle of interrogation of the M-mode beam was carefully aligned at the anteroposterior axis to be perpendicular to the LV walls, and LVEDD, IVST, and PWT were measured by the leading edge method. LVESD was measured at the time of maximum anterior motion of the posterior wall. LV fractional shortening (FS) was calculated from the M-mode recordings using the following equation: FS (%) = [(LVEDD-LVESD)/LVEDD] x 100. Two-dimensionally guided pulsed Doppler recordings of LV transmitral flow were obtained from the apical four-chamber view. To obtain the transmitral flow, the sample volume was placed just below the mitral valve leaflets. The sample volume was then placed between the mitral valve and LV outflow tract so the aortic valve closure line and the onset of mitral flow could be clearly identified. Isovolumic 1 relaxation time (IVRT) was taken as the time from aortic valve closure to the onset of mitral flow. To minimize influence of heart rate, IVRT was divided by square root of RR interval (IVRTcor). Velocity of circumferential shortening (VCF) was measured using the formula: (LVEDD-LVESD)/(LVEDDxET), where ET is the ejection time. LV outflow velocity pattern was recorded from the apical long-axis view, with the sample volume positioned just below to the aortic valve. Myocardial Performance Index (MPI) is the ratio of total time spent in isovolumic activity (isovolumic contraction time and isovolumic relaxation time) to the ejection time (ET). These Doppler time intervals were measured from the mitral inflow and LV outflow time intervals. Interval “a”, from the cessation to onset of mitral inflow, is equal to the sum of the isovolumic contraction time, ET and isovolumic relaxation time. Ejection time “b” is derived from the duration of the LV outflow Doppler velocity profile. The MPI was calculated using the formula: (a-b)/b. Both M-mode and Doppler tracing were recorded at a sweep speed of 200 mm/s, and images were stored on videotape for off-line analysis. To measure simultaneous heart rate, single channel electrocardiography was performed for at least three consecutive RR intervals with the electrodes placed on the upper and lower limbs of the animal. 2