The invention is a valve deactivator assembly (15) for use in connection with a valve train of an internal combustion engine. In application, a pre-selected number of the engine cylinders would each be equipped with a deactivator connected to its intake engine valve. Upon driver selection or predetermined road conditions, sufficient lost motion would be introduced into the valve train so that the valve would remain closed and the cylinder deactivated as the engine is in operation. The deactivator has in its inner body (19) a latch assembly that is in a latched condition for normal operation of the valve train. When it is desired to retain the valve in the closed position and deactivate a cylinder, the latch assembly is caused to be moved to the unlatched condition by increase in the pressure of the engine oil. When the latch assembly is unlatched, significant lost motion is introduced into the valve train causing the valve to remain closed and the cylinder is deactivated.