The cardiopulmonary bypass is then initiated by inserting a cannula into the ascending aorta as distally from the aortic root as possible while still supplying all arterial branches, another cannula is inserted into the right atrium, and a vent is created for the left ventricle via catheterization of the right superior pulmonary vein. The HLM is started at a low-flow and the patient's body is cooled to a rectal temperature of 20 °C (68 °F), which prevents the brain damage otherwise associated with the temporary circulatory arrest necessary during the procedure; the patient must be cooled for a minimum of 20 minutes prior to beginning the repair.