Abstract: An alternating pressure pad, useful between a mattress and a bed-ridden person for preventing the occurrence of bed sores, defines two separate sets of interdigitated transverse inflatable body support chambers. The support chambers are alternately inflated and deflated to provide alternating areas on his body where a person lying on the pad is supported by the pad. In a leg and foot section of the pad, the support chambers have a smaller inflated diameter than the other chambers of each set to provide effective support, and freedom from support, of the heel and ankle areas of the body when those chambers are alternately inflated at a pressure consistent with comfort of the person. A body air chamber is defined in the pad over and independent from the support chambers under a pad top sheet which has a predetermined portion of its area open for air to flow through it.