Max

Max is Peter and his ex-wife, Eden's dog.

Season 2
When Lou and Peter are spending time together at the Dude Ranch, Peter gets a phone call. He becomes worried about someone's health, when he realises it's not serious he tells Lou that it's his father-in-law. He continues on the phone to tell the person to pack up Max's things and he'll pick him up. When he hangs up the phone he realises Lou has gone. When they meet up for Peter to explain, Lou is angry that he's married. He clarifies that he's divorced when Max jumps out the carriage and leaps onto Lou. She realises that Max is his dog not his kid, he assures her that he'd tell her if he had kids. (Full Circle)

Season 3
Peter brings Max with him to Heartland for Ty's surprise leaving party for going away to university. When Lou sends Peter on a beer run, he takes Max with him. (Broken Arrow) When Peter goes fishing for the weekend with Tim, Jack and Ty he asks Lou to watch him as he's not great at camping. When she's working at the Dude Ranch Max wanders off and tries to befriend a porcupine who in return sticks him full of quills. They call Scott and he works to remove them and assures them he'll be fine. (Catch and Release)