A blood reservoir comprises a rigid casing and a perforated tubular member positioned within the casing and extending between the edges thereof. An inlet aperture is at a position at the upper end of the reservoir in communication with the bore of the tubular member while an outlet aperture is positioned adjacent the bottom of the casing exterior to the tubular member. The bore of the tubular member contains first blood-defoaming means, and the tubular member carries a blood filter. In accordance with this invention, second blood defoaming means are positioned about the exterior of the tubular member to dissipate the fine bubbles without interference from the larger bubbles, which have been previously removed by passage through the first blood defoaming means.