Strumming Pattern: dduudu 
When you play it with chords it goes like this:
C9 (dd) C (uudu) x2
Am4 (dd) Am (uudu) x2
Dm9 (dd) Dm (uudu) x2
G x2


Intro: C9/C, C9/C, Am4/Am, Am4/Am, Dm9/Dm, Dm9/Dm, G, G

C9/C           C9/C
Last Christmas I gave you my heart
Am4/Am                Am4/Am
But the very next day you gave it away
 Dm9/Dm       Dm9/Dm
This year to save me from tears
  G                  G
I'll give it to someone special.


It goes through the hole song.
That's it, have fun.
p.s. I'm pretty sure those are correct chords