A system comprising: electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient; and computing apparatus comprising processing circuitry and coupled to the electrode apparatus and configured to: monitor electrical activity of the patient's heart using one or more electrodes of the plurality of external electrodes during left ventricular-only pacing therapy delivered, by an implantable medical device, at a plurality of different A-V intervals over a plurality of different heart rates of the patient and during biventricular pacing therapy delivered, by the implantable medical device, at a plurality of different A-V and V-V intervals over a plurality of different heart rates of the patient, generate electrical heterogeneity information, EHI, from the monitored electrical activity from the electrode apparatus, wherein the EHI is representative of one or both of mechanical cardiac functionality and electrical cardiac functionality, select an A-V interval for left ventricular-only pacing therapy for each different heart rate based on the EHI generated from the monitored electrical activity during left ventricular-only pacing therapy, and select an A-V interval and a V-V interval for biventricular pacing therapy for each different heart rate based on the EHI generated from the monitored electrical activity during biventricular pacing therapy. electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient; and computing apparatus comprising processing circuitry and coupled to the electrode apparatus and configured to: monitor electrical activity of the patient's heart using one or more electrodes of the plurality of external electrodes during left ventricular-only pacing therapy delivered, by an implantable medical device, at a plurality of different A-V intervals over a plurality of different heart rates of the patient and during biventricular pacing therapy delivered, by the implantable medical device, at a plurality of different A-V and V-V intervals over a plurality of different heart rates of the patient, generate electrical heterogeneity information, EHI, from the monitored electrical activity from the electrode apparatus, wherein the EHI is representative of one or both of mechanical cardiac functionality and electrical cardiac functionality, select an A-V interval for left ventricular-only pacing therapy for each different heart rate based on the EHI generated from the monitored electrical activity during left ventricular-only pacing therapy, and select an A-V interval and a V-V interval for biventricular pacing therapy for each different heart rate based on the EHI generated from the monitored electrical activity during biventricular pacing therapy. monitor electrical activity of the patient's heart using one or more electrodes of the plurality of external electrodes during left ventricular-only pacing therapy delivered, by an implantable medical device, at a plurality of different A-V intervals over a plurality of different heart rates of the patient and during biventricular pacing therapy delivered, by the implantable medical device, at a plurality of different A-V and V-V intervals over a plurality of different heart rates of the patient, generate electrical heterogeneity information, EHI, from the monitored electrical activity from the electrode apparatus, wherein the EHI is representative of one or both of mechanical cardiac functionality and electrical cardiac functionality, select an A-V interval for left ventricular-only pacing therapy for each different heart rate based on the EHI generated from the monitored electrical activity during left ventricular-only pacing therapy, and select an A-V interval and a V-V interval for biventricular pacing therapy for each different heart rate based on the EHI generated from the monitored electrical activity during biventricular pacing therapy.