An energy efficient system is described for delivering electrostimulation to a patient's heart. The system may be configured to switch, in some cases dynamically, between a multi-site electrostimulation configuration and a single-site electrostimulation configuration for delivering electrostimulation to a single heart chamber (e.g. left ventricle) based upon one or more triggers and/or a predefined schedule to reduce the energy expenditure of the system while still providing the benefits of multi-site electrostimulation.