Inclusion Criteria:  In a stable condition on the same disease specific medication >4 weeks. Signed informed consent. Patients with left-heart disease  Exclusion Criteria:  Severe daytime hypoxemia (pO2 ≤7.3 kPa or <55 mmHg). Other clinically significant concomitant disease states (e.g., renal, hepatic dysfunction, etc.). Inability to follow the procedures of the study, e.g. due to language problems, psychological disorder, dementia or confusional state of the subject, neurological or orthopedic problems with inability to ride a bicycle. Woman with known pregnancy (Women with known pregnancy will not be allowed into the study. It will however not be searched for early unknown pregnancy in woman of child-bearing potential, as cycling is not contraindicated in early unknown pregnancy stage and we thus do not plan routine pregnancy tests before study entrance in women of childbearing potential). Enrolment into another clinical trial with active treatment.