Abstract Inappropriate therapy due to noise oversensing caused a true ventricular fibrillation (VF) and a life-threatening event in a patient. A 19-year-old patient with surgically corrected congenital heart disease and systolic dysfunction had an implantable cardioverter defibrillator implanted for primary prevention in 2013. This patient was admitted at the Emergency Department in June 2018 after receiving eight shocks from the device on the same day, with a prolonged syncope after the third shock. Another noise-induced VF detection occurred, and two inappropriate shocks followed sequentially, causing true VF. Four appropriate shocks were subsequently needed until sinus rhythm was finally restored.