Mackenzie Hart, played by Morgan Brittany, was a character seen on Melrose Place, the second series of the Beverly Hills, 90210 continuity. She appeared in the season 3 double-length finale The Big Bang Theory.

Mackenzie was the owner and founder of Mackenzie Hart Design and her husband, Richard Hart, was the president. She and Richard met with Jane Andrews after her business went under and she was not very kind to Jane, putting down her choice of clothing and calling her 'Janet'. However, Richard hired her and they began having an affair.

Mackenzie was not happy with him seeing other people, but agreed to let him do it because she wanted him to be happy. However, she let him keep his job as long as he performed his husbandly duties.

She was killed when Kimberly Shaw blew up 4616 Melrose Place