Cardiopulmonary resuscitation, or CPR, is an emergency medical procedure used on humanoids who are victims of either cardiac or respiratory arrest. CPR provides artifical blood circulation and respiration until a person spontaneously recovers, is placed on a life support system, or dies.
During the final battle with Khan Noonien Singh, an overloaded helm console seriously injured Commander Hikaru Sulu, stopping his heart. Doctor David Marcus performed CPR on Sulu until medics could arrive and take Sulu to sickbay, saving Sulu's life in the process. (TOS novelization: Star Trek II: The Wrath of Khan)
When the Srivani were experimenting on the USS Voyager's crew, Roberta Luke was one of those most seriously affected by the Srivani's genetic modifications. Because of the genetic modifications, Luke collapsed on the bridge. Captain Kathryn Janeway attempted to perform CPR on the young woman, but was unable to save her life. (VOY episode: "Scientific Method")