A device consisting of an endocardial electrode with an ultrasound transducer intended to be implanted within the left ventricle of the heart to receive ultrasound (US) pulses from a parent transmitter and convert these into electrical pacing impulses to pace the left ventricle for cardiac resynchronization therapy (CRT) with a separate co-implanted pacemaker. It consists of a small electrode with a transducer intended to be attached to the endocardium. It is intended as an alternative to left-ventricular pacing using a coronary venous pacing lead. Disposable devices dedicated to implantation (e.g., delivery catheter) may be included.