An apparatus may include an implantable therapy circuit that provides bi-ventricular pacing to a subject, a heart sound signal sensing circuit that produces a sensed heart sound signal that is representative of at least one heart sound associated with mechanical cardiac activity, a memory circuit to store one or more heart sound templates of cardiac capture, and a comparison circuit that compares a segment of the sensed heart sound signal to the one or more heart sound templates of cardiac capture to identify ventricles in which cardiac capture was induced by the bi-ventricular pacing. In some situations, an indication of the ventricles in which cardiac capture was induced may be generated according to the comparison.