Heater Control Valve

I recently noticed that my heater control valve was leaking anti-freeze again
(I replaced it approximately 4 years ago, just after purchasing the truck.  
When I went to get a replacement, the guy at O'Reilly's asked me if the
arrow on the valve was pointing toward the firewall or away from the firewall.  
I went out and checked and it was pointing away from the firewall.  It was
only after purchasing the new valve that I remembered replacing this valve
four years ago and this question didn't come up.  When the guy showed me
the pictures of the valves on the computer, the only difference was the
direction of the arrows on the body of the valve.  Does anyone know which
one my truck needs?  The one with the arrow pointing toward the firewall or
the one pointing away from the firewall.  Any insight is greatly appreciated.