Which way does the water from engine run to heater core in my 1970 Chevy Nova?

In a 1970 Chevy Nova, the coolant flows from the engine to the heater core in a series configuration. This means the coolant flows from the engine, *through* the heater core, and then back to the engine. It doesn't split off into separate branches; it's a single continuous loop. The heater valve controls whether coolant flows through the heater core or bypasses it.