Watch the Re-Voice online guitar lesson by Brad Carlton from Chord Studies: i to V7 Vamps Vol. 1
This progression is in the key of A minor. We're starting on Am our I chord and then moving to the V chord which is E7. Notice how on the second time through we re-voice the E7 chord. This brightens the chord up because we've got the ♭7, the D note on the second string.