Dyspnea (breathlessness) on exertion is the most prevalent and distressing symptom of heart failure (HF). Nevertheless, the mechanisms of dyspnea in HF remain poorly understood. Thus, the general aim of this pilot study is to advance our understanding of the mechanisms of activity-related dyspnea in patients with HF. Studies will be performed in patients with mild, moderate and severe HF (n=24) as well as in healthy, age- and sex-matched control subjects (n=8). We will test the hypothesis that the increased prevalence and severity of activity-related dyspnea in HF reflects the interaction between an exaggerated drive to breathe and the inability of the respiratory system to meet this increased demand. Detailed physiological and perceptual responses to bicycle exercise will be examined and compared, first, between HF patients and healthy control subjects and, second, across patients with varying degrees of HF severity. The results from this preliminary study will be used to help design future studies in this patient population.