This is a proof of concept trial using ranolazine, a medication, in patients with known Coronary Artery Disease and reduced left ventricular function, EF < 40%. We propose that ranolazine therapy will result in demonstrative improvements in cardiac function that can be objectively assessed using the parameters measured with CPET. We propose that demonstrative improvement in CPET parameters on ranolazine will translate into improved patient outcomes for this patient population.