Universal pacing and defibrillation system

An implantable universal pacing and defibrillating system provides efficacious sensing, pacing, and cardioversion/defibrillation in all four chambers of the heart. The system includes three leads with one lead being configured for implant in the coronary sinus for sensing, pacing, and defibrillating in both the left atrium and left ventricle. The leads also provide a plurality of different electrode configurations for both ventricular and atrial defibrillation. Sequential primary and secondary defibrillation shocks may be employed to advantage for depolarizing essentially all of the ventricular or atrial myocardium.