Apparatus is provided for performing ablation of cardiac tissue using ultrasound. The apparatus includes a beacon, adapted to be placed at a cardiac site in a body of a subject. The apparatus further includes a set of ultrasound transducers, each transducer adapted to detect a respective ultrasound signal coming from the beacon. Each transducer is adapted to output a time-reversed ultrasound signal, reversed in time with respect to a property of at least one of the beacon signals, and configured to ablate the cardiac tissue.