Background: The vast majority of infants born with congenital heart disease (CHD) reach adulthood because of the developments in cardiology in recent decades. This thesis aims to describe the psychosocial situation of child/adolescent cardiac patients and their families, investigate the situation faced by parents and siblings initially and over time, investigate the approaches paediatric cardiologists use in encountering the family, and describe the teamwork occurring in paediatric cardiology teams (PCTs) in Sweden. Theoretical framework: The theoretical framework was based on a quality of life model applied to children, a stress-coping model, and a psychosocial approach including support, profession, and teamwork. Methods: The research combines quantitative data collection/analysis and qualitative research interviews/content analysis. Results: Complexity: The three grades of medical complexity differed regarding the number and severity of psychosocial symptoms, the children with the most complex CHD having the most severe symptoms. The most frequent symptoms in the whole patient group regarding various spheres were: healthcare and treatment-related needs in the external sphere, family symptoms in the interpersonal sphere, and mental/psychosomatic symptoms in the personal sphere. Coping: Being informed of a child’s/sibling’s heart disease has emotional consequences, so information, communication, and support are essential. Breaking the news of a child’s disease can be described as a turning point still significant after ten years. The professionalism of the doctor’s approach in breaking the news is crucial. Profession: Among paediatric cardiologists, how to break bad news to a family is an important concern, evident in findings regarding the significance of trust and confidence and the use of various emotional positions. Paediatric cardiologists commonly wish to be skilled at handling this situation, and attaining the needed skills calls for reflection, education, and sharing experience. Team: PCTs in Sweden aim and try to work in a structured way. In PCTs, there is a need for leadership, resource coordination, coaching, and a forum for joint reflection. Dependence on the physician on the team was identified in all PCTs. The challenge of managing increasing complexity at both the family and system levels requires interprofessional teams. Conclusions: These studies illustrate the psychosocial complexity and the need of psychosocial support. Emotional consequences, communication, information and support are essential both for the children, parents/families and for the professionals. To manage this complexity organizational alteration action plans are required. There is a need for a forum to stimulate dialogue and common reflection in the local PCT and at the regional and national centres.