Cavis

From Tardis Wiki, the free Doctor Who reference

Cavisadoratrelundar (or Cavis) and her partner Gandar were agents of Celestial Intervention Agency recruited from the Patrexes College and totally loyal to Lady President Romana. She had been on over 30 missions without regenerating and therefore only had one heart. She also had messy blond hair. Cavis died when she was decapitated and stabbed in both hearts (presumably to stop the other heart from growing) so she wouldn't regenerate. (EDA: The Shadows of Avalon)