In this paper a new model for studying cardio-renal reflex dynamics has been introduced. Such models are important since by understanding cardio-renal dynamics well, better total artificial heart (TAH) implants may be designed and/or better drug treatment plans may be developed for helping TAH patients. The model introduced combines relevant parts of the two cardiovascular system models developed previously by Guyton et. al. A simulation of total surgical cardiac denervation (a condition which results in TAH implants), has resulted in an increase in the blood volume below the experimentally observed values. A correction of the kidney model including the effect of the renal sympathetic nerve activity on the set point of the tubulo-glomerular feedback mechanism is suggested.