A system and methods of using a multi-lumen catheter and a blood pump to increase cardiac output and blood oxygenation are described. The system diverts deoxygenated blood from the right atrium to the left atrium, through the atrial septum. The catheter is adapted for simultaneously pumping blood to and from a patient's heart. A gas exchanger may be used as part of the system to remove CO2 and add o2 to the blood that is pumped via the system. Components or portions of the system may be implantable in the patient.
