Patient commenced on cardiopulmonary bypass, flow/line pressure normal, on bypass just over 1 minute venous blood appeared very blue as did arterial blood, had just cross clamped and cardioplegia just running, informed surgeon and anaesthetist problem with blood gas blender. FiO2 at 60%, and gas flow at 2.5L, on commencing bypass. Adjusted FiO2 to 100%, and gas flow to 10L, palpated end of air/O2 line with finger, very little air/O2 going into oxygenator. Traced line back to vaporiser, large tear observed on tubing at back of he vaporiser, line seemed perished. Anaesthetist put tape/sleek on tubing and a tie wrap, which solved problem. Poor oxygenation for over 2minutes, blood gases were pO2=6.7kPa, PCO2=6.8kPa. Repeat blood gases after the repair were PO2=53.2kPa, PCO2=7.2kPa. Adjusted FiO2 and gas flow then repeated blood gases were PO2=29.6kPa, PCO2=4.5kPa. Case continued without incident, exited CPB without problem.