Cardiopulmonary Exercise Testing (CPET) is a diagnostic tool used to assess the function of the heart and lungs during physical activity. It typically involves a patient exercising on a treadmill or stationary bike while their heart rate, oxygen consumption, and carbon dioxide production are monitored. This helps healthcare providers evaluate a person's cardiovascular and respiratory fitness. The results of CPET can help identify underlying health issues, such as heart disease or lung disorders, and guide treatment plans. It is often used for patients with unexplained shortness of breath, those preparing for surgery, or athletes looking to optimize their performance.