In this paper we describe a laser Doppler velocimeter (LDV) with an optical fiber that measures blood flow velocities accurately in a small sample volume. The principle, optical arrangement, spatial and the temporal resolutions and accuracy for blood flow measurements are delineated, followed by a report of the results of measurements of coronary artery and vein blood flow velocities in dogs. Finally, we touch upon some recent progress made in the LDV with an optical fiber pickup.