Methods Patients receiving a pacemaker for sick sinus syndrome (n=20) with an LV ejection fraction <40% will be randomly allocated to receive either conventional RV pacing or LV pacing via the coronary sinus. Serial 2D and 3D transthoracic echocardiography will be performed before implantation, one day post implantation, then at 1 week, 1 month, 6 months and 1 year. The primary endpoints will be new onset TR and the diagnosis of at least moderate TR. Other endpoints include biventricular function, ventricular dyssynchrony, complications of device implantation, mortality and major cardiovascular events.