Abstract: A blood treatment apparatus having within a sealed housing a chamber for mixing oxygen and blood, a column of packed beads through which the mixture of oxygen and blood passes to cause oxygenation of the blood, a blood defoamer through which the oxygenated blood must pass, a reservoir into which the defoamed blood passes and a heat-exchanger which occupies a substantial portion of the lower region of the reservoir. The heat-exchanger comprises a stacked array of spirally wound coils being connected at each of its ends to a manifold which is external of the sealed housing. The configuration of the various components and of the walls of the sealed housing are such that the coils provide high heat-exchange effectiveness by optimizing the size and uniformity of the spacing between coils through which the blood must pass.