The invention concerns a hydraulic valve actuator for reciprocating engine comprising at least a hydraulic cylinder (3) for opening at least one valve (2) via at least one valve opening selector (11) by means of at least one hydraulic positive displacement pump (4) whereof the hydraulic fluid supplied at the output can be forced into a high pressure circuit (10) by at least one pump outlet closure (8), said valve (2) capable of being maintained opened by means of an opening non-return valve (24), then of being reseated by means of a valve closing selector (25) which directs the hydraulic fluid contained in the hydraulic cylinder (3) in the hydraulic positive displacement pump (4) input by co-operating with a pump input non-return valve (26).