The optimal site at which to pace the right ventricle (RV) is still unclear. This study aimed to answer this question utilising cardiac magnetic resonance imaging, which up until recently was contraindicated in pacemaker patient cohorts. The objective was to determine the effect of apical and outflow tract septal pacing on cardiac function and remodeling as assessed by MRI. In addition, physcial and psychological functional parameters were assessed. A series of sub-studies were performed as part of the research. Study 1 validated the velocity phase encoding used to determine flow measurements. This found measurements were reproducible. Study 2 and 3 focused on the method of CPEX testing in pacing dependent patients and whether a training effect was observed with the CPEX testing. It found that treadmill testing resulted in a greater heart rate response and higher VO2 max results. No significant training effect was observed. Study 4 used phantom models to determine the effect of metal susceptibility artefact on mapping and velocity encoded MR sequences. An inverse relationship between artefact and distance from the pacemaker was observed. At approximinately 10 cm from the device, artefact is negligible. Study 5 determined the best methods of image optimization in the presence of the pacemaker. T1 weighted imaging along with spoiled gradient imaging was less affected by artefact compared to late gadolinium and bSSFP imaging. Study 6 evaluated in-house developed software to measure torsion using data derived from commercial available tagging and feature tracking software. At low heart rates measures were comparable but tagging became less accurate with heart rates over 100 bpm. The main study comprised of the baseline data of 50 patients from the ongoing MAPS trial and some intermediate data after 9 months for a smaller cohort. There was not a significant difference in left ventricular volumes or ejection fraction at baseline but differences were observed in deformational indices including longitudinal strain, strain rate, twist and torsion. At 9 months a difference in ejection fraction was observed between the pacing modes along with differences in deformational parameters. Clinically significant differences were not seen between pacing positions at baseline or 9 months but the outflow tract septal position was superior based on deformational data.