Open-label, multi-center extension study of intravenous ARC-520 in combination with entecavir or tenofovir in patients with chronic HBV infection. Patients who successfully completed the Heparc-2002/Heparc-2003 studies and responded to therapy are eligible to participate. Patients who have signed a Human Research Ethics Committee approved informed consent and have met all of the protocol eligibility criteria will continue receiving daily oral entecavir or tenofovir and IV injections of ARC-520. Study visits will occur once every 4 weeks for a total of 9 visits for monitoring and ARC-520 administration .