There is provided a calf compression device for reducing the risk of deep vein thrombosis which comprises an inflatable cuff (100, 200) adapted to be wrapped around the whole or part of a calf of a human person and a pump (104, 204) capable of first inflating the cuff (2) and then deflating the cuff over a regular repeating cycle, said repeating cycle comprising rapidly inflating the cuff (100, 200) to a pressure of between 40 and 70 mm mercury above ambient, maintaining the pressure for 10 to 15 seconds, deflating the cuff (100, 200) over a period of 40 to 50 seconds and then repeating the cycle by rapidly inflating the cuff (100, 200) within 10 seconds of commencement of the cycle.