Pressure - Volume (PV) analysis is the de facto standard for assessing myocardial function. Conductance based methods have been used for the past 27 years to generate instantaneous left ventricular (LV) volume signal. Our research group has developed the instrumentation and the algorithm for obtaining PV loops based on the measurement of real - time admittance magnitude and phase from the LV of anaesthetized mice and rats. In this study, the instrumentation will be integrated into an ASIC (Application Specific Integrated Circuit) and a backpack device will be designed along with this ASIC. This will enable measurement of real-time in vivo P-V loops from conscious and ambulatory rats, useful for both acute and chronic studies.