Subjective and objective limitations to exercise and activity are hallmarks of heart failure (HF), regardless of underlying ejection fraction (EF). These limitations relate to cardiovascular abnormalities involving the systolic and diastolic properties of the heart, venous, and arterial vasculature, as well as noncardiovascular abnormalities, including impairments in pulmonary function, autonomic regulation, anemia, metabolism, and changes in mitochondria and skeletal muscle. The contribution of these abnormalities varies between patients with HF with preserved EF and those with HF with reduced EF, but, even within each HF subtype, there is substantial individual patient pathophysiologic variability, which suggests a potentially important role for phenotyping based on exercise reserve responses to individualize treatment. In this article, we review the current understanding of exercise reserve limitation with a focus on specific organ systems involved, both in patients with HF with preserved EF and HF with reduced EF, and how these interact to lead to symptoms of exercise intolerance and objective limitations in submaximal and peak aerobic capacity across the spectrum of HF.