A 23-year-old female with familial long-QT syndrome and a 48-year-old male with familial dilated cardiomyopathy were given an implantable cardioverter-defibrillator (ICD) as prophylaxis. About half a year after the implantation, there was an appropriate and successful ICD-discharge in both patients in connection with ventricular tachycardia. Treatment with an ICD can be life-saving in patients with cardiac rhythm disorders. The most common indication is ventricular tachycardia or fibrillation due to ischaemic heart disease, but an ICD may also be indicated in patients with cardiomyopathy, congenital heart disease, hereditary arrhythmia or a planned heart transplantation.