An apparatus for determining cardiac performance in the patient includes a plurality of electrodes adapted to be placed in the patient and in communication with a heart chamber of the patient for measuring conductance and blood volume in the heart chamber of the patient; and a processor for determining instantaneous volume of the ventricle based on measurement of complex admittance at a plurality of frequencies to identify mechanical strength of the chamber, the processor in communication with the electrodes. A method for determining cardiac performance in a patient.