A multilumen catheter that maximizes the blood flow into and out of the patient's vasculature while also providing for passive and/or active perfusion of tissue downstream of where the catheter resides in the vasculature. The inventive catheter comprises a proximal end, a first distal and a second distal end. Lumens extending from the proximal end to each of these distal ends provide for blood circulation within one or between two blood vessels. At least one aperture in one of the lumens positioned near the proximal end provides for active perfusion of blood to the patient's vasculature downstream of where the aperture resides in the vasculature when the catheter is inserted into the patient for treatment. The inventive catheter may comprise a third lumen positioned entirely within the patient's vasculature, providing passive perfusion of blood to the patient's vasculature downstream of where the third lumen resides in the vasculature when the catheter is inserted into the patient for treatment.