This study aims to evaluate the effect of sauna therapy on congestion levels during cardiac rehabilitation in patients with heart failure who have an impaired or moderately impaired ejection fraction, compared to standard cardiac rehabilitation care. To investigate this, patients with reduced cardiac function who are hospitalized as part of a cardiac rehabilitation program will be included. These patients will be randomly assigned to two groups: standard cardiac rehabilitation program (control group) and sauna group (intervention group). The study will also assess whether this approach could allow for a reduction in the dose of diuretics, which are commonly used to remove excess fluid, thereby helping to avoid certain side effects. The expected benefits include a reduction in symptoms such as shortness of breath and swelling, improvements in quality of life and physical fitness, and enhanced blood vessel function.