Cardiopulmonary Exercise Testing in Congenital Heart Disease: A Never-Ending Story from Paediatrics to Adult Life.

Cardiopulmonary exercise testing (CPET) is increasingly recognized as a key tool for evaluating patients with congenital heart disease (CHD). While traditional assessments focus on resting parameters, CPET provides dynamic, integrated insight into cardiovascular, respiratory, and muscular function during exertion. This review explores the clinical value of CPET across the spectrum of CHD, with dedicated focus on its applications in both adult and paediatric populations. We analyse the prognostic significance of key CPET parameters-particularly peak oxygen consumption (peak VO), ventilatory efficiency (VE/VCO slope), and heart rate dynamics-within distinct anatomical and physiological categories of CHD. CPET reliably detects exercise intolerance, guides intervention timing, informs exercise prescription, and stratifies risk. Peak VO and heart rate reserve are consistently associated with adverse outcomes across most CHD types. However, the prognostic utility of other variables, such as the VE/VCO slope, varies with pathophysiology-being less reliable in cyanotic lesions like Eisenmenger syndrome. In paediatric patients, CPET must be adapted to growth-related physiological variability and is increasingly used to assess quality of life, functional limitation, and response to therapy. CPET is a powerful, non-invasive tool that should be integrated into routine management of CHD patients across all ages. It enhances risk assessment, supports tailored care, and promotes safe physical activity, ultimately contributing to improved long-term outcomes and quality of life.