The health mechanic varies between games. In the main House of the Dead series, the spin-off Loving Deads: The House of the Dead EX, and the spiritual successor Vampire Night, lives are used; whereas in the arcade version of The House of the Dead 4: Special, Zombie Revenge and The House of the Dead: Overkill, a health bar is used instead.
Health in the main House of the Dead series is chiefly referred to as lives. Life icons have traditionally been represented by lit torches or flames (in Vampire Night, it is represented by crosses). By default, the player starts with 3 lives, and usually can have a maximum of 5 (or 9 in some games). When the player takes damage from a creature, or accidentally shoots a civilian, a life is lost. When all have been lost, the player can choose to continue or end the game via time up (in The House of the Dead 4: Special, there are no continues for the arcade version).
Bonus lives can be earned by rescuing civilians, collecting first aid kits hidden in environments, or scoring a high grade (typically an A or S rank) at the end of a level.