heater hose on a/c truck

[incoma]

I've forgotten and don't have any "before" pictures of this particular item. I'm connecting my heater shutoff valve in my heater hose running from the intake to heater core. Which direction does the water flow? The valve has an arrow on it, but I'm not sure which way to install it.

If I can get this one last piece figured out, I can fire my beast up. Help!!

I've attached a pic for reference..which way should the arrow point - to the intake or to the heater core.