Investigating the performance of a novel cardiovascular implantable electronic device (CIED) capable of natural (physiological) pacing of the heart. A new cardiac ultrasound (echocardiography) analysis technique, known as Global Longitudinal Strain (GLS), will be used to assess the performance of cardiac contraction during this physiologic pacing.

Patients with an implanted physiologic pacemaker will undergo programmed pacing for their device whilst a transthoracic echocardiogram (TTE) ultrasound is performed to collect data on cardiac performance. Participants will be recruited at anytime after the physiologic pacemaker has been implanted (the variable of interest is the ventricular contraction resulting from preferential pacing via programming, not the duration since implant). The A 12-lead electrocardiogram (ECG) will be recorded to monitor cardiac rhythm with ECG electrodes (3M red dots) attached to the participant as per standard ECG protocol. The continuous ECG monitoring will ensure fidelity of the pacing performed and the reliability of intrinsic rhythm. The pacemaker will be programmed (by an accredited cardiac device specialist technician or electrophysiology cardiologist) to; - preferential pace the physiologic pacing lead - preferential pace the other cardiac lead - preferentially allow intrinsic activation This will be the same experience a patient would usually have for routine annual device checks when capture thresholds are tested. As beat to beat performance will be evaluated, no 'wash out' period will be required between pacing protocols. TTE ultrasound (performed by a registered medical sonographer) will be performed by routine standard with conventional imaging techniques. The session of data collection (ECG, CIED programming and TTE ultrasound) is expected to last less than 60 minutes and will only be performed for one session. The ultrasound data will be analyzed after the data collection session has been completed. TTE analysis technique of global longitudinal strain (GLS) will be used to assess the ventricular contraction performance. Pooled analysis of the TTE data will be used to address the study hypothesis.