Hi & Welcome to HCM. I appreciate your concern for your beloved son. Safety of Slendertone kit in a patient with aortic stenosis depends on the degree of stenosis or insufficiency. It is not recommended if the aortic valve disease is severe. Physical activity is not restricted in asymptomatic patients with mild aortic stenosis. Patients with moderate aortic stenosis should avoid competitive sports that involve high dynamic and static muscular demands. Other forms of exercise can be performed safely, but it is advised to evaluate him with an exercise test before he starts using Slendertone. Hope to have answered your query.