A hydraulic unit (5) for a cylinder head (2) of an internal combustion engine with a hydraulic, variable valve train (1) is provided. In the hydraulic unit, a high-pressure chamber (11), a medium-pressure chamber (12), and also a low-pressure chamber (16) used as a hydraulic medium reservoir are formed. The low-pressure chamber communicates merely via a choke opening (17) with the medium-pressure chamber, wherein the choke opening passes through a separating wall (18) extending between the low-pressure chamber and the medium-pressure chamber.