A medical device system for selecting a pacing site, comprising: a plurality of electrodes (140, 142, 144, 148, 150, 158, 162, 166) arranged to produce a signal of electrical heart activity and for delivering cardiac pacing pulses to a plurality of pacing sites along a heart chamber; a sensor for producing a signal of mechanical heart activity; a processor means configured to determine baseline mechanical heart activity from the sensor signal and baseline electrical heart activity from the signal of electrical heart activity, determining from the signal of mechanical heart activity a change from the baseline mechanical activity during pacing at each of the plurality of pacing sites and to determine from the signal of electrical heart activity a change from the baseline electrical activity during pacing at each of the plurality of pacing sites; a processor sorting means for sorting the plurality of pacing sites in a first order based upon the changes in mechanical heart activity and in a second order based upon the changes in electrical heart activity; and a processor selecting means for selecting a pacing site from the plurality of pacing sites as a common pacing site between the first order and the second order; wherein the processor sorting means is configured to reject a pacing site from the first order resulting in a change in the mechanical heart activity not meeting a threshold change and to reject a pacing site from the second order resulting in a change in the electrical heart activity not meeting a threshold change and thereafter to select a pacing site from the first order and the second order having an overall highest ranking in the first order and the second order when more than one pacing site is common to the first order and the second order. a plurality of electrodes (140, 142, 144, 148, 150, 158, 162, 166) arranged to produce a signal of electrical heart activity and for delivering cardiac pacing pulses to a plurality of pacing sites along a heart chamber; a sensor for producing a signal of mechanical heart activity; a processor means configured to determine baseline mechanical heart activity from the sensor signal and baseline electrical heart activity from the signal of electrical heart activity, determining from the signal of mechanical heart activity a change from the baseline mechanical activity during pacing at each of the plurality of pacing sites and to determine from the signal of electrical heart activity a change from the baseline electrical activity during pacing at each of the plurality of pacing sites; a processor sorting means for sorting the plurality of pacing sites in a first order based upon the changes in mechanical heart activity and in a second order based upon the changes in electrical heart activity; and a processor selecting means for selecting a pacing site from the plurality of pacing sites as a common pacing site between the first order and the second order; wherein the processor sorting means is configured to reject a pacing site from the first order resulting in a change in the mechanical heart activity not meeting a threshold change and to reject a pacing site from the second order resulting in a change in the electrical heart activity not meeting a threshold change and thereafter to select a pacing site from the first order and the second order having an overall highest ranking in the first order and the second order when more than one pacing site is common to the first order and the second order.