Guidelines for patients having first-time implants advocate that even when heart function is only mildly impaired, modern pacing approaches should be utilised to avoid the potentially damaging effects of RV pacing to preventing symptoms from pacing induced or worsened cardiomyopathy. However, once a traditional (RV) pacemaker is implanted, development of impaired heart function does not prompt a device upgrade. Even at the end of battery life, physicians simply replace it like-for-like. This trial tests whether such patients have better symptoms and quality of life if changed to a modern physiological pacing strategy from the traditional RV pacing approach. In this crossover trial, participants will be upgraded to a physiological pacing strategy. After their procedure, they will have a one-month run-in period to recover from the procedure (their pacemaker will be programmed to continued RV pacing). They will be have 2 one-month blinded time periods, randomised to physiological pacing or right ventricular pacing alternately. They will subsequently undergo two six-month blinded randomised time periods. Patients will document symptoms monthly on a mobile phone application or computer. At the end of each time period, they will have measurements of heart function, a walking test and quality-of-life questionnaires including the SF-36 questionnaire. The investigators hypothesise that upgrading to physiological pacing strategies will improve patients' quality of life.