A device for measuring the blood flow of a body tissue comprises a catheter having a catheter head for the insertion into the inside of a body tissue and a center piece having a light emission surface, out of which an optical conductor leads, and having a reflection surface, which is disposed opposite of the light emission surface and oriented obliquely to the longitudinal axis of the optical conductor. The optical conductor is disposed such that an emitted light beam is directed at the reflection surface, the emitted light beam can be deflected at the reflection surface and reflected into the body tissue, and a reflected light beam can be reflected out of the body tissue at the reflection surface and fed into the optical conductor. The catheter head is divided into an insertion region and a connecting region, wherein the insertion region comprises a plurality of recesses on the surface thereof. In the direction of the connecting region, the insertion region has an increasing diameter. The recesses are provided in the insertion region such that webs are formed in the direction of the connecting region between the recesses along the surface of the catheter head.