Inclusion Criteria:  Indication for implanting of a single chamber ICD (primary or secondary prevention) according to current guidelines; Sustained sinus rhythm as the current prevalent atrial rhythm; Planned de novo implantation with a BIOTRONIK single chamber DX ICD system; Patient is able to understand the nature of study and to provide written informed consent; Patient is willing and able to perform all follow up visits at the study site; Patient is willing and able to use the CardioMessenger and accepts the BIOTRONIK Home Monitoring concept.  Exclusion Criteria:  Age < 18 years Any limitation to contractual capability; Female patients who are pregnant or breast feeding or planning pregnancy during the course of the study; Known active malignant disease or recovered from malignant disease within 2 years prior to enrollment; Life expectancy < 2 years; Patient is participating in any other interventional clinical investigation.