The most common use for the harmonic minor scale is over the V dominant 7th chord (referred to as V7) in a minor key. For those of you who aren't familiar with chord theory, the V7 chord in a minor key is seven frets up from the first chord in the key. For example, in the key of Aminor, the V7 chord is E7 (the note E is seven frets up from A). In the key of Eminor, the V7 chord would be B7.
Technical Note For Theory Geeks Only:
Playing a harmonic minor scale over the V7 chord outlines a V7(b9,b13) chord. This scale will NOT work over an unaltered 9th chord.

