Scott Cardinal is Heartland's veterinarian and close friend to the Fleming/Bartlett family.
Background
Scott has a long history with the Fleming/Bartlett family as one of Marion's "projects", having been where Ty is now as a troubled teen living in the barn loft. As teenagers, he and Lou had a huge crush on one another, which resurfaced once she returned home from New York when her mother died. But after some time dating they broke up. Though as seen in later episodes Scott still had feelings for Lou.