1984 Dodge Aries Heat doesn't work/car broke down smoking

My son's car lost it's heat about 2 weeks ago. I thought it was the thermostat but have not looked at the car yet. Today his car needed a jump and started quickly. About 15 minutes later he called with a broken down car that he said was smoking from the engine, he heard some hissing and the car died. He said the cold/hot guage needle was moving back and forth but ended up on hot. I askled him to open the hood and check for a wet engine to see if it overheated and he said the engine was dry. What do you think it might be?