Surgical correction of congenital heart defects in children requires the utilization of cardiopulmonary bypass, a technique that temporarily substitutes heart and lung functions during surgery. During this process the patient´s circulation is controlled by a bypass machine which provides several functions:

1. Controls the patient's blood flow by pumping of blood in the patient's body.
2. Controls the correct oxygen levels in the patient's blood.
3. Regulates the temperature and fluid level of the blood. This process triggers negative responses in the heart and throughout the whole body, potentially resulting in injury to the heart and other organs such as brain, kidneys and lungs.

Remote ischaemic preconditioning (RIPC) describes a procedure that could potentially reduce the injury to heart muscle during cardiac surgery. The procedure consists of the inflation of a blood pressure cuff on the child's leg for three 5 minute cycles. This process acts by briefly reducing blood flow to the leg muscle, which will then activate the body´s own protective mechanisms and thereby reduce heart injury.

Several animal studies have been used to help the understanding of the mechanisms behind this process, and trials in human adults have showed optimistic results; however evidence regarding the paediatric population is limited and necessary since children present different basal profiles, risks and requirements.

The investigators propose a randomized clinical trial assessing the efficacy of RIPC to provide protection against injury to the heart and other organs in children going through cardiac surgery using CPB at the Royal Hospital for Sick Children. The research project will have a translational approach, integrating basic molecular mechanisms to clinical outcome. The investigators hope it will allow the understanding and utilisation of the patient´s own protective mechanisms, reducing CPB-related injury and ultimately improving patient outcome.

Inclusion Criteria:

• Children undergoing cardiac surgery for correction of congenital heart defects utilizing cardiopulmonary bypass and cold blood cardioplegia strategy of myocardial protection.
• Children whose parents understand the child's condition, the purpose of the study and are willing to participate.

Exclusion Criteria:

• Children whose parents either are unwilling or do not have sufficient understanding of the study.
• Emergency operations, where there is insufficient time to establish the study protocol.
• Premature children presenting a corrected gestational age under 35 weeks.
• Presence of extracardiac abnormalities, apart from cases of Down and DiGeorge syndromes which will be included.
• Patients with known viral blood infections (e.g. HIV, Hepatitis B) or severe congenital infection.
• Patients with severe preoperative brain injury.