Heart failure (HF) is a complex syndrome characterized by myocardial dysfunction, derangement of multiple organ systems and poor outcome. Out of several markers of severity, abnormalities in exercise ventilation (VE) offer relevant insights into the pathophysiology of dyspnea, lung gas exchange, and control of ventilation and are now recognized as meaningful indicators of disease severity and prognosis. Ventilation inefficiency, identified as an increased slope of VE vs carbon dioxide production (VCO₂) recognizes as major determinants an increased waste ventilation due to enhanced dead space, early occurrence of lactic acidosis, and an abnormal chemoreflex and/or metaboreflex activity. In some cases of HF, especially associated with advanced hemodynamic and neural deregulation, an exercise oscillatory ventilatory (EOV) pattern may occur. According to an increasing number of studies, EOV identifies the 15–30 % of higher-risk HF patients requiring aggressive treatment and provides an even more robust prediction of outcome compared to VE/VCO₂ slope. Overall, a refined prevalence definition and more comprehensive use of these markers in a clinical environment and in future interventional trials seem challenging for the years to come.