Abstract: An apparatus for correlating the respiratory and cardiac cycles includes a circuit for defining a chosen period in the progress of the respiratory cycle as the end of a regulatable delay beginning when the ascending front of the inspiratorial pressure reaches a regulatable level as well as a circuit for defining a chosen period in the progress of the cardiac cycle as the end of a regulatable delay beginning when the differential dV/dt of the blood pressure reaches a regulatable level. An operator such as a terminal relay is activated upon the coincidence of these two periods in time after a regulatable delay and during a regulatable period.