The purpose of this study is to to assess the effect of ATV 300 mg BID on the PK of raltegravir 400 mg BID, to assess the effect of raltegravir 400 mg BID on the PK of ATV 300 mg BID, and to assess the ECG effects of ATV 300 mg BID over 21 days, given with or without raltegravir 400 mg BID.