An implantable system providing cardiac anodal stimulation (AS) as a system for effecting hyperpolarization of myocardial cells of a heart chamber to enhance the relaxation thereof in the diastolic phase and to thereby enhance cardiac function. The AS system is optimally timed to be delivered in an AS delivery interval following an AS delay interval timed from a preceding ventricular depolarization or pacing pulse to effect maximal cardiac relaxation. The sub-threshold AS pulse or train of pulses is increased in energy (amplitude) and/or decreased in energy to and from a peak energy level gradually rather than abruptly. The AS characteristics are optimized in an initialization process that determines the AS characteristics that provide the optimum blood pressure parameters and thereafter continually or from time to time in a confirmation process. Confirmation of the AS characteristics is determined by measuring one or more blood pressure parameter in the right atrium or ventricle reflecting the blood pressure in the heart chamber subjected to the AS pulses and comparing the measured blood pressure parameter to the corresponding optimum blood pressure parameter determined in the initialization process. The initialization process is repeated if the comparison shows a deterioration in cardiac function response to the AS. The AS pulse waveforms are preferrably delivered through a plurality of discrete AS electrodes distributed about the heart chamber or through or large surface area epicardial patch or endocardial AS electrodes.