(ii) Methods for protecting against other sources of bias All patients referred to our Arrhythmia Service will be assessed for suitability to take part in this study. Once recruited, study subjects will be block randomised in a 1:1 fashion to either conventional right ventricular lead implantation or left ventricular coronary sinus lead implantation. They will be blinded to their allocation during the course of this study to remove any bias.