Objective To investigate the key factors for PV Loop evaluation in rats and to improve this method. To provide examples of cardiac function measurements obtained from normal rats and from rats with cardiac hypertrophy induced by transverse aortic constriction (TAC). To establish a more reliable method for rats heart measurements. Methods Rats underwent left ventricular catheterization through the right carotid artery. Through adjustments of the position of the pressure-volume conductance catheter, the optimal PV Loops and a number of cardiac functional parameters were acquired. The key influencing factors, calibration of volume, position of the catheter in the left ventricle (LV) and suspension of ventilator were assessed. Results 1. The real volume of left ventricle were acquired by injecting appropriate volume of hypertonic saline through jugular vein, which deducted the parallel conductivities of ventricular wall. 2. To get better PV loops, it's important to adjust the position of the catheter in the left ventricle until all of the pressure and volume sensors were located in the ventricle as well as out of touch with the ventricular wall. 3. Suspension the ventilator during the test is conducive to stable and reasonable data acquisition. We further assessed the cardiac functions of healthy rats and rats with cardiac hypertrophy with this improved method, which showed better performances. Conclusions This study we have evaluated the influences of calibration of volume, position of the catheter in the left ventricle (LV) and ventilator on measurements of rats PV loops, and further improved this method. Moreover, we have validated this method with measurements of cardiac functions of normal rats and cardiac hypertrophic rats.