An implantable device and associated method for delivering multi-site pacing therapy is disclosed. The device comprises a set of electrodes including a first and second left ventricular electrodes spatially separated from one another and a right ventricular electrode, all coupled to an implantable pulse generator. The processing circuit coupled to the implantable pulse generator, the processing circuit configured to determine whether a prospective heart failure condition has occurred and if so to trigger the pulse generator to switch from a first pacing mode to a second pacing mode, the first pacing mode comprising delivering only a first pacing pulse to a left ventricle (LV) and thereafter delivering an RV pacing pulse to the right ventricular electrode within a single cardiac cycle and the second pacing mode comprising delivering first and a second pacing pulses to the LV and thereafter delivering an RV pacing pulse to the right ventricular electrode within a single cardiac cycle.