Sienna Hearn (born 16 July 2002) is an Australian water polo player. She was part of the Australian women's water polo team that finished in second place at the 2024 Summer Olympics.
She competed at the 2022 FINA Women's Water Polo World League Intercontinental Cup, 2023 Tri Nations Water Polo Test Match Series, and 2024 World Aquatics Championships.
She played for UTS Balmain Tigers. She trains with the New South Wales Institute of Sport.