A sterile, mechanical regulator used in a cardiopulmonary bypass system, particularly systems employing centrifugal pumps during open-heart surgery. It typically provides unidirectional flow to prevent inadvertent backflow of blood and air into the heart, and/or controls the pressure within the system (e.g., maintains gentle suction to prevent line collapse during left ventricular venting, or controls the vacuum from suctioning of the heart or the surgical field). This is a single-use device.