To provide a highly reliable device for treating the cardiac disease wherein a tissue to be treated is completely altered after an energy is emitted to the tissue, in particular an ablation device.

An ablation device comprising an ultrasonic transducer 1 and an applicator 7 disposed adjacently to the ultrasonic transducer 1 to form an intracardiac energy output is provided. The measurement of the echocardiographic thickness of the myocardium M can be carried out through the transducer 1. Further, the device comprises a controlling means, this controlling means is to regulate the energy output from the applicator 7 and and this energy output can be carried out so as to be adjusted to the measured thickness of the myocardium.