A wireless system for stimulating the left ventricle of a heart of a human subject having left bundle branch block, LBBB, the system comprising: a controller-transmitter configured to be implanted in the human subject, the controller-transmitter including: one or more sensors configured to receive an indication of electrical conduction of the heart , a controller operably coupled to the one or more sensors and configured to determine, in substantially real-time, an occurrence of an onset of a QRS segment in the electrical conduction of the heart , and a first transducer operably coupled to the controller and configured to emit an acoustic signal in response to the controller determining the occurrence of the onset of the QRS segment in electrical conduction of the heart ; and a receiver-stimulator configured to be implanted adjacent to the left ventricle of the human subject, the receiver-stimulator including: a second transducer configured to (a) receive the acoustic signal emitted from the first transducer and (b) convert the received acoustic signal into electrical energy, and one or more stimulation electrodes coupled to the second transducer and configured to deliver the electrical energy to the left ventricle of the heart as electrical stimulation; wherein the system is configured to synchronize contraction of the left ventricle and a right ventricle of the heart by delivering the electrical stimulation to the left ventricle within a predefined duration beginning at the onset of the QRS segment in the electrical conduction of the heart . a controller-transmitter configured to be implanted in the human subject, the controller-transmitter including: one or more sensors configured to receive an indication of electrical conduction of the heart , a controller operably coupled to the one or more sensors and configured to determine, in substantially real-time, an occurrence of an onset of a QRS segment in the electrical conduction of the heart , and a first transducer operably coupled to the controller and configured to emit an acoustic signal in response to the controller determining the occurrence of the onset of the QRS segment in electrical conduction of the heart ; and one or more sensors configured to receive an indication of electrical conduction of the heart , a controller operably coupled to the one or more sensors and configured to determine, in substantially real-time, an occurrence of an onset of a QRS segment in the electrical conduction of the heart , and a first transducer operably coupled to the controller and configured to emit an acoustic signal in response to the controller determining the occurrence of the onset of the QRS segment in electrical conduction of the heart ; and a receiver-stimulator configured to be implanted adjacent to the left ventricle of the human subject, the receiver-stimulator including: a second transducer configured to (a) receive the acoustic signal emitted from the first transducer and (b) convert the received acoustic signal into electrical energy, and one or more stimulation electrodes coupled to the second transducer and configured to deliver the electrical energy to the left ventricle of the heart as electrical stimulation; a second transducer configured to (a) receive the acoustic signal emitted from the first transducer and (b) convert the received acoustic signal into electrical energy, and one or more stimulation electrodes coupled to the second transducer and configured to deliver the electrical energy to the left ventricle of the heart as electrical stimulation; wherein the system is configured to synchronize contraction of the left ventricle and a right ventricle of the heart by delivering the electrical stimulation to the left ventricle within a predefined duration beginning at the onset of the QRS segment in the electrical conduction of the heart . <EOS>