ICD therapy has been believed to be a last resort therapy for preventing of sudden death due to VT/VF. Since 1980, when clinical use first began, ICD therapy has rapidly increased in use in Europe and in the United State. In Japan, in 1990 clinical investigation began, and in 1996 it received insurance reimbursement. From here on, it should experience a rapid rise in use. However there are many problems such as complications, inappropriate shocks, size, longevity and psychological effects etc. Therefore indication for their use should be carefully considered and it is very important to obtain the patient's informed consent.