The purpose of this study is to reconstruct a 12-lead electrocardiogram (ECG) from intracardiac (IC) electrograms (EGM) obtained from defibrillator devices (ICD). The purpose of such a reconstruction is to allow the use of IC EGM for diagnosis of clinical conditions for which ECG have historically been used, and to test the feasibility of a reconstruction technique for the standard 12-lead or extended electrocardiogram from electrical potentials obtained from inside a patient.

Reconstructing a 12-lead surface ECG from intracardiac EGM vectors of patients implanted with defibrillators can be of great value. It allows implantable devices that have thus far been used exclusively for arrhythmia detection and treatment, to be used for diagnostic purposes in similar ways as the ECG. The advantage of the reconstruction process is that it provides real-time continuous monitoring, which can be used for multiple purposes, including but not limited to:

1. Ischemia detection
2. Myocardial Infarction detection
3. Electrolyte abnormalities detection
4. Assessment of effect of medications
5. Improved rhythm discrimination

Inclusion Criteria:

1. Subjects must be at least 18 years of age.
2. Subjects must be referred for ICD implantation or already have an ICD implanted..
3. Subjects must be willing to sign informed consent.

Exclusion Criteria:

1. Subject is unable or unwilling to sign informed consent.
2. Subject is pacemaker dependent.
3. Subject is pregnant as indicated by standard clinical procedures prior to implant.

Subjects will be identified by their cardiologist who is also an investigator on this study at the time they are evaluated for an ICD implantation. Once it has been determined during the course of the patient's regular clinical care that he or she requires an ICD, they will be approached for enrollment into the study by the physician investigator and the clinical research coordinator.