The goal of this observational study is to learn about functional heterogeneity of immune cells before and after cardiopulmonary bypass (CPB) in children with congenital heart disease (CHD). The main question[s] it aims to answer are:

• Does CPB cause immune paralysis after CHD surgery?
• How does the functional heterogeneity of immune cells change before and after CPB in children undergoing CHD surgery? Participants will receive 3ml of peripheral blood before CPB, 2 hours after CPB, and 3 days after CPB, and the peripheral blood samples will be sequenced by single cell to explore the immune heterogeneity before and after CPB.

CPB-induced immune paralysis is the main cause of postoperative infection in CHD, which seriously affects the prognosis of children. The underlying mechanism of CPB-induced immune paralysis has not been fully determined. This study intends to use scRNA-seq to describe gene transcription profiles of immune cells in peripheral blood of children undergoing CHD surgery before and after CPB, and explore the differences within and between different immune cell populations including T cells and the changes of immune cells in different sequences. To fill the gap in the study of immune mechanism in CPB-induced immune paralysis microenvironment at single-cell resolution.

Inclusion Criteria:

1. Birth weight range: 2500-6000g;
2. Operation duration >90min;

Exclusion Criteria:

1. preterm infants or preoperative infections;
2. systemic immune diseases and serious complications: such as rheumatoid arthritis, systemic lupus erythematosus, severe liver and kidney function damage, leukemia, etc.;
3. Patients who have received an organ transplant;
4. Patients who have received immunomodulatory drugs: patients who have received immunomodulatory drugs before surgery;
5. Parents refused to participate or were unable to provide sufficient samples: Parents or legal guardians refused to participate in the study.

In this study, children aged 31d-1y who underwent subCPB ventricular septal defect repair for the first time between January 2024 and February 2024 at the Children's Hospital Affiliated to Zhejiang University School of Medicine were enrolled. This study will comply with the requirements set out in the Declaration of Helsinki and will be approved by the Ethics Committee of our Institute.