A steerable catheter includes an elongate cannula having a proximal end and a distal end. A blood characteristic sensor, such as an oxygen sensor, is connected to the cannula and disposed to sense percent oxygen saturation of blood at the distal end of the cannula. The blood oxygen sensor generates a signal indicative of percent oxygen saturation. An oximetry display is responsive to the signal and capable of displaying sensed percent oxygen saturation in a form understandable by an operator. A steering mechanism is operably connected to the cannula and is selectively operable by an operator to deflect the distal end of the cannula. A method of locating the coronary sinus of a heart involves endovascularly introducing a catheter into the right atrium, sensing percent oxygen saturation at the distal end of the catheter, and steering the catheter toward a region of lowest percent oxygen saturation.