An apparatus for treating or preventing valvular stenosis, the apparatus comprises: - a ultrasound probe (2,6) located externally to a heart of patient, able to produce ultrasound waves focused inside said heart and suitable to generate, at a focal spot, a pressure sufficient to result in cavitation, - an imaging device for mapping in real time a treatment region (A, C) of a cardiac valve of the patient, said treatment region comprising at least one leaflet of the cardiac valve, - a controller (5, 7, 8) configured for driving the ultrasound probe to emit a sequence of focused ultrasound waves, the controller being further configured for estimating in real-time a motion of the treatment region from images acquired by said imaging device, and for steering the focused ultrasound waves emitted by the ultrasound probe in function of said motion of the treatment region to scan the entire treatment region; characterized in that the apparatus further comprises a measuring device suitable for measuring an index of valvular stenosis after the ultrasound probe is controlled to emit the sequence of N focused ultrasound waves, the controller being further configured for reiterating the steps of controlling the ultrasound probe to emit a sequence of focused ultrasound waves and measuring said index of valvular stenosis until said index crosses a predefined threshold. - a ultrasound probe (2,6) located externally to a heart of patient, able to produce ultrasound waves focused inside said heart and suitable to generate, at a focal spot, a pressure sufficient to result in cavitation, - an imaging device for mapping in real time a treatment region (A, C) of a cardiac valve of the patient, said treatment region comprising at least one leaflet of the cardiac valve, - a controller (5, 7, 8) configured for driving the ultrasound probe to emit a sequence of focused ultrasound waves, the controller being further configured for estimating in real-time a motion of the treatment region from images acquired by said imaging device, and for steering the focused ultrasound waves emitted by the ultrasound probe in function of said motion of the treatment region to scan the entire treatment region; characterized in that the apparatus further comprises a measuring device suitable for measuring an index of valvular stenosis after the ultrasound probe is controlled to emit the sequence of N focused ultrasound waves, the controller being further configured for reiterating the steps of controlling the ultrasound probe to emit a sequence of focused ultrasound waves and measuring said index of valvular stenosis until said index crosses a predefined threshold. the controller being further configured for estimating in real-time a motion of the treatment region from images acquired by said imaging device, and for steering the focused ultrasound waves emitted by the ultrasound probe in function of said motion of the treatment region to scan the entire treatment region; characterized in that the apparatus further comprises a measuring device suitable for measuring an index of valvular stenosis after the ultrasound probe is controlled to emit the sequence of N focused ultrasound waves, the controller being further configured for reiterating the steps of controlling the ultrasound probe to emit a sequence of focused ultrasound waves and measuring said index of valvular stenosis until said index crosses a predefined threshold.