Methods and systems are disclosed for determining whether a patient is a responder to cardiac resynchronization therapy. The beginning and ending of the intrinsic ventricular depolarization are determined through signals measured from one or more electrodes implanted in the patient's heart. An interval between the beginning and ending of the intrinsic ventricular depolarization is computed and is compared to a threshold. The threshold may be determined empirically. The pacing parameters of a heart stimulation device, such as a pacemaker, may then be configured, for example, by setting the paced atrio-ventricular delay based on whether the patient responds positively to cardiac resynchronization therapy.