An implantable medical device for delivery of cardiac therapy to a patient, the device comprising: electrode apparatus comprises at least one left ventricular electrode (44, 45, 46, 47)configured to be located proximate the left ventricle of a patient's heart and at least one right ventricular electrode configured to be located proximate the right ventricle of a patient's heart; a therapy delivery module configured to deliver pacing therapy using the electrode apparatus; a sensing module configured to sense electrical activity of the patient's heart using the electrode apparatus; and a control module coupled to the therapy delivery module and to the sensing module and characterised in that the control module is configured to: deliver one or more left ventricular paces to the patient's left ventricle with a cross-chamber pacing vector using a selected left ventricular electrode of the at least one left ventricular electrode and a selected right ventricular electrode of the least one right ventricular electrode, wherein the selected left ventricular electrode is the cathode and the selected right ventricular electrode is the anode in the cross-chamber pacing vector; measure one or more first cross-chamber sense times between the one or more left ventricular paces and one or more right ventricular senses in response to the one or more left ventricular paces; deliver one or more right ventricular paces to the patient's right ventricle using the selected right ventricular electrode; measure one or more second cross-chamber sense times between the one or more right ventricular paces and one or more left ventricular senses in response to the one or more right ventricular paces; and determine whether anodal capture of the right ventricle is occurring when delivering ventricular pacing with the cross-chamber pacing vector based on the measured one or more first cross-chamber sense times and the measured one or more second cross-chamber sense times. electrode apparatus comprises at least one left ventricular electrode (44, 45, 46, 47)configured to be located proximate the left ventricle of a patient's heart and at least one right ventricular electrode configured to be located proximate the right ventricle of a patient's heart; a therapy delivery module configured to deliver pacing therapy using the electrode apparatus; a sensing module configured to sense electrical activity of the patient's heart using the electrode apparatus; and a control module coupled to the therapy delivery module and to the sensing module and characterised in that the control module is configured to: deliver one or more left ventricular paces to the patient's left ventricle with a cross-chamber pacing vector using a selected left ventricular electrode of the at least one left ventricular electrode and a selected right ventricular electrode of the least one right ventricular electrode, wherein the selected left ventricular electrode is the cathode and the selected right ventricular electrode is the anode in the cross-chamber pacing vector; measure one or more first cross-chamber sense times between the one or more left ventricular paces and one or more right ventricular senses in response to the one or more left ventricular paces; deliver one or more right ventricular paces to the patient's right ventricle using the selected right ventricular electrode; measure one or more second cross-chamber sense times between the one or more right ventricular paces and one or more left ventricular senses in response to the one or more right ventricular paces; and determine whether anodal capture of the right ventricle is occurring when delivering ventricular pacing with the cross-chamber pacing vector based on the measured one or more first cross-chamber sense times and the measured one or more second cross-chamber sense times. deliver one or more left ventricular paces to the patient's left ventricle with a cross-chamber pacing vector using a selected left ventricular electrode of the at least one left ventricular electrode and a selected right ventricular electrode of the least one right ventricular electrode, wherein the selected left ventricular electrode is the cathode and the selected right ventricular electrode is the anode in the cross-chamber pacing vector; measure one or more first cross-chamber sense times between the one or more left ventricular paces and one or more right ventricular senses in response to the one or more left ventricular paces; deliver one or more right ventricular paces to the patient's right ventricle using the selected right ventricular electrode; measure one or more second cross-chamber sense times between the one or more right ventricular paces and one or more left ventricular senses in response to the one or more right ventricular paces; and determine whether anodal capture of the right ventricle is occurring when delivering ventricular pacing with the cross-chamber pacing vector based on the measured one or more first cross-chamber sense times and the measured one or more second cross-chamber sense times.