Hospital admission for decompensated heart failure marks a critical inflection point in a patient’s health. Despite the improvement in signs or symptoms during hospitalization, patients have a high likelihood of readmission, reflecting a lack of resolution of the underlying condition. Surprisingly, no studies have characterized the cardiorespiratory fitness of such patients. Fifty-two patients (38 [73%] male, age 57 [52 to 65] years, left ventricular ejection fraction 31% [24 to 38]) underwent cardiopulmonary exercise testing 4 (1 to 10) days after hospital discharge, when stable and without overt signs of volume overload. Transthoracic Doppler echocardiography, measurement of N-terminal pro-B-natriuretic peptide, and quality of life were also assessed. Aerobic exercise capacity was severely reduced: peak oxygen consumption (pVO2) was 14.1 (11.2 to 16.3) ml/kg/min. Ventilatory inefficiency as indicated by the minute ventilation carbon dioxide production relation (VE/VCO2 slope) >30 and oxygen uptake efficiency slope <2.0 was noted in 41 (77%) and 39 (75%) patients, respectively. Forty-five (87%) patients had 1 of 2 high-risk features (pVO2 < 14 ml/kg/min or VE/VCO2 >30). Perceived functional capacity, measured by the Duke Activity Status Index, was also severely reduced and correlated with pVO2. N-terminal pro-B-natriuretic peptide levels and early transmitral velocity/early mitral annulus velocity (E/e’) ratio at echocardiography showed a modest correlation with lower pVO2. In conclusion, patients with recently decompensated systolic heart failure demonstrate severe impairment in cardiorespiratory fitness, severely limiting quality of life.