Abstract: A fully portable, semi-automatic mechanical heart-lung substitution system and method. The system includes a venous cannula adapted for insertion into the vena cava of the patient and an arterial cannula adapted for insertion into the right and/or left common carotid artery of the patient. The venous cannula is attached to a roller pump used to pump blood from the patient's right heart to a membrane oxygenator. The speed of the roller pump is automatically controlled by means of a pressure sensor that is attached to the outer wall of the venous cannula so as to sense the internal venous blood pressure inside the patient's vena cava. Blood flows from the oxygenator to a compliance reservoir which expands so as to create increasing pressure within the reservoir as the volume of blood filling the reservoir increases.