Peripheral response in heart failure patients Heart failure is a complex condition that affects the functioning of the heart and compromises a person's ability to perform physical activities. Did you know that patients with chronic heart failure (CHF) encounter limitations at different levels when it comes to exercise? With this study, we aimed to explore these limitations and shed light on how CHF patients respond to physical activity. Therefore, we investigated two key aspects: the body's oxygen response and the oxygen (O2) levels within muscle and brain tissues. The first concept refers to the body's overall physiological response to consuming and utilising oxygen during physical activity. This involves the cardiovascular system’s ability to deliver oxygen to the working muscles and the muscle’s capacity to use oxygen to produce energy. The second concept refers to the O2 levels specifically in the muscles itself. It measures the amount of oxygen available in these specific tissues during exercise, reflecting the oxygen delivery and utilization process to support their proper function and metabolism (i.e. energy demand). These aspects are crucial in understanding the impact of heart failure on exercise capacity, which is the ability to perform physical activity without experiencing fatigue. We could gain valuable insights into how the severity of the disease affects patients' exercise capacity by evaluating the relationship between the severity of the disease and various physiological markers measured during exercise. Therefore we measured the physiological response of CHF patients during an incremental cycling test while measuring oxygen in peripheral tissues of the muscle and the brain. While the oxygen response is normally investigated using whole body measurements, these are the result of peripheral responses in the working muscles and organs. Our initial findings suggest the importance of analyzing responses at different levels to fully understand these patients’ limitations and thereby highlight the significance of peripheral aspects of CHF patients’ exercise. By expanding the scope of this research, we can unravel more differences in physiological responses among CHF patients of varying disease severity. Ultimately, this research paves the way for more targeted and effective strategies in managing CHF and improving the quality of life for these patients.