- Not to be confused with Heather from The Black Book, Heather Wilson from The Garfield Show, or Heather Kerr, the actress.
St. Clair has long, straight blonde hair with two strands that hang onto her face. Facially, she also has light green eyes, singular eyelashes, and wears pink lipstick. While at the beach, she wears a sapphire colored top, a same-colored bathing suit bottom, white socks, and blue sneakers.
While driving and flying, she wears a long-sleeved sapphire jersey with a white collar, a lengthened cerulean colored pants, and the same shoes as before. As she prepares to jump out of the plane, she wears a sapphire one-piece suit, a same-colored helmet with a vertical white stripe, white gloves, dark brown shoes, a gray belt, and a parachute.
In the mountains, she wears a sapphire jersey with a white collar, sapphire pants, a cerulean belt with a lighter colored buckle, sapphire mitts, dark blue and gray skiing shoes, and a white and sapphire long hat.
She is shown to be dedicated to getting exactly what she wants, doing extreme activities, just to achieve her goal. She has been seen to be careless on multiple occasions: driving recklessly on the road, flying an airplane with minimal knowledge (as well as skipping a lesson for her fingernails), skydiving, and skiing. She also seems to be charming, shown when she was able to persuade Jon to ski. Heather also claims to like men who are "mature".
While at the beach, Jon Arbuckle sees Heather doing a photoshoot on the pier. After finishing, she spots Garfield through a tower viewer, and declares she must have him. After Maurice, the photographer, asks if Jon will part with Garfield, Heather claims that she is able to get anything she pleases. She then approaches Jon, and asks him if he'd like to come away with her. After privately celebrating, Jon agrees to go with her, before she requests he bring Garfield.
Later and while recklessly driving on the roads, she claims that she'd like to take Arbuckle and Garfield to her place in the mountains via an airplane. After Jon claims the airport to be the opposite way, she reveals that she has her own private airplane. After arriving at the airplane, they take off with her flying. She reveals that she hasn't gotten to the lesson about turbulence, and that she skipped her landing lesson. Afterward, she decides to leave the plane via a parachute, declaring that she feels invigorated.
After Jon and Garfield both land from their parachute, she manages to coax Jon into go skiing with her, much to Garfield's dismay. While skiing, Jon claims they aren't meant for eachother, before he and Garfield fly into a snow pile. After climbing out, Jon declares that they aren't meant for one another before she requests that she get something to remember him by: his cat. Jon refuses, claiming that Garfield and him are inseparable which angers Heather, who declares she was only going out with him for Garfield. After talking about friendship, Arbuckle and Garfield find that she has moved onto a mountain man, with the intentions of getting his goat.
- Like several other characters, Heather has a tendency to get Jon's name wrong.
- In the Pasta Wars episode of The Garfield Show, Jon dreams of a model named Heather. This is a possible allusion to Heather St. Clair.
- The character and name of Heather St. Clair may be a parody of Heather Locklear.