We conducted a national, single center (Hospital Clínico Universitario de Valladolid, Spain, Valladolid), prospective study of patients with prior hospitalization because of COVID-19 who were admitted between March 1st, 2020, and May 15th, 2020. All eligible patients underwent at least at first-time follow-up from the index event. Exclusion criteria were age < 18 years old, pregnant women, terminally ill patients, active SARS-CoV-2 infections, inability to exercise and previous known severe pulmonary or heart disease. Patients underwent a clinical assessment for symptom burden, questionnaire for quality of life (Kansas City Cardiomyopathy Questionnaire and SF-36), venous blood sampling, 6-minute walking test (6-MWT), tests of lung function (spirometry and diffusing capacity of the lungs for carbon monoxide) and treadmill cardio-pulmonary exercise testing (CPET). 48-hours before the test of lung function and the CPET, all patients yielded a negative result in the reverse transcription-polymerase chain reaction (RT-PCR) for SARS-CoV-2. For definitive analysis patients were assigned to the control group if they did not refer dyspnea at the time of the follow-up, a small asymptomatic out-patient control group without prior hospitalization was also included.