An intravascular device for locating a coronary sinus of a patient's heart and method of using the same. In one embodiment, the intravascular device includes an elongated member having at least one lumen and at least one optical fiber coupled to the elongated member. The optical fiber has a distal end configured to contact with a blood flow within the patient's heart and a proximal end coupled to a laser Doppler velocimetry system for performing a plurality of laser Doppler velocity measurements of the blood flow within the heart to locate the coronary sinus of the heart. Incorporating LDV technology into an intravascular device such as a catheter or a guidewire system provides diagnostic information of the physiologic environment of the lesion before, during, or after a therapeutic procedure.