A device constricts vessels and includes a constricting belt and a lock. One end of the constricting belt is arranged in a fixed manner in the lock and one end of the constricting belt is movably arranged in the lock. The constricting belt and the lock include a material having a smooth surface. In a closed state, the lock is a smooth, cube-shaped or elongated body, which includes no further external openings or projections apart from the feedings for the constricting belt.
