A minor7th chord is created by adding a flattened 7th degree to any minor chord. For example, a Cm7 chord contains the notes C, Eb, G and Bb (1, b3, 5 and b7). Here are some common open minor 7th chord shapes.
Dm7
Ebm7
Em7
Fm7
F#m7
Gm7
Bm7
Cm7
Dbm7
Abm7
Am7
Bbm7