This is a randomized, open-label, active-controlled study whose primary objective is to evaluate the safety and efficacy of several doses of GS-7340. This study will evaluate the safety, viral kinetics, and antiviral activity of 4 different doses of GS-7340 over 28 days of therapy. In addition, the study will evaluate the antiviral activity of an optimal dose of GS-7340 versus 300mg Tenofovir disoproxil fumarate (TDF) over 28 days of therapy.