Abstract: An improved blood oxygenator including a first chamber having a plurality of oxygenator tubes disposed therein with each tube having an elongated cross-section. A blood inlet for introducing blood and a oxygen inlet for introducing oxygen gas into the blood are located on the oxygenator such that a mixture of blood and oxygen flows through the tubes where the blood is oxygenated. A blood foam exits from the tubes and then flows through a ring of reticulated polyurethane causing the blood to be further oxygenated. A defoamer is disposed about the first chamber and defoams the blood. The blood is then filtered and collected in a reservoir and can be withdrawn from the oxygenator through a blood outlet port.