This study is looking at children who weigh between 3.5 and 12 kilograms and need heart surgery. The surgery uses a machine called a cardiopulmonary bypass, which helps the heart and lungs during the operation. The study wants to see if kids have fewer problems and recover faster if they don't receive extra blood during their surgery. The researchers think children not receiving extra blood might spend less time in the ICU (Intensive Care Unit) and the hospital.

Children can join if they are having planned or urgent heart surgery and fit into certain categories called STS STAT categories 1-4, which rate the complexity of their condition. Kids who weigh more than 12 kg or less than 3.5 kg, need emergency surgery, or have other serious conditions cannot join.

• The study compares outcomes between children receiving blood and those who do not.
• Participants must weigh 3.5-12 kg and not be in emergency situations.
• There are no mentions of compensation or specific visit requirements.