Conductance measurements to generate an instantaneous left ventricular (LV) volume signal in the mouse are limited by the volume signal being a combination of blood and LV muscle. Only the blood signal is desired. We developed a conductance system that operates at two simultaneous frequencies to identify and remove the myocardial contribution to the instantaneous volume signal. This system is based on the observation that myocardial resistivity varies with frequency while blood resistivity does not. To calculate LV blood volume using the dual frequency conductance system in mice, in vivo murine myocardial resistivity is measured and combined with an analytic approach. The goals of the present study were to identify and minimize the sources of error in the measurement of myocardial resistivity, in order to enhance the accuracy of the dual frequency conductance system. We extend these findings to a gene- altered mouse model to determine the impact of measured myocardial resistivity on the calculation of LV pressure-volume (PV) relations. We examine the impact of temperature, the timing of the measurement during the cardiac cycle, background strain, anisotropy, and intra-measurement and inter-animal variability on the measurement of intact murine myocardial resistivity. Applying this knowledge to diabetic and non-diabetic mice ages 11 and 20-24 weeks, we demonstrate differences in myocardial resistivity at low frequencies, enhancement of LV systolic function at 11 and LV dilation at 20-24 weeks, and histology and electron microscopy studies demonstrating greater glycogen deposition in the diabetic mice. This study demonstrates an accurate technique of measuring myocardial resistivity and its impact on the determination of LV PV relations in gene-altered mice.