Abstract: A filter device for a cardiotomy reservoir comprises multiple layers of concentric, tubular elements with a central passage for supply of blood, purified by passage through the device. A first, inner element for defoaming the blood comprises a porous sponge material within a second element comprising a depth filter medium for filtering the blood. The depth filter is surrounded by a third element of porous sponge material spacing apart the depth filter and the outer, fourth element, a fine-filter screen for removing substantially all remaining, undesirable particulate matter in the blood.