A method and system of cardiac pacing is disclosed. A baseline rhythm is determined using a plurality of body-surface electrodes. A set of baseline functional electrical metrics is determined in response to determining the baseline rhythm. Resynchronization pacing is delivered using a right ventricular electrode and a pacing left ventricular electrode or only with a left ventricular electrode. A set of functional electrical metrics relating to cardiac depolarization and repolarization is determined in response to resynchronization pacing. A determination is made as to whether relative reduction of at least one functional electrical metric from the set of functional electrical metrics exceeds X % of its corresponding value from the set of baseline functional electrical metrics. A determination is made as to whether an absolute value of at least one electrical metric from the set of the functional electrical metrics is less than Y ms. A determination is made as to whether a site is responsive to cardiac resynchronization therapy (CRT).