In this study, it is aimed to investigate the effects of a cardiac rehabilitation program consisting of two different aerobic exercise modalities on aerobic capacity, symptoms, quality of life, and sarcopenia in patients with heart failure who present with one or more symptoms such as dyspnea, difficulty walking, muscle weakness, or limitations in activities of daily living and who are in need of cardiac rehabilitation.

Patients who were followed up in the Heart Failure Clinic, aged 18-75, had stable clinical symptoms, and were referred to Cardiopulmonary Rehabilitation Unit for the cardiac rehabilitation program and met the inclusion criteria will be included in our study.

Prior to initiating the program, participants will be prescribed an individualized exercise regimen determined to be both effective and safe, based on their exercise capacity assessed through the CPET-derived optimal exercise prescription. For the MCT group, the program includes a 5-minute warm-up at 30% of VO₂max, followed by 20 minutes of continuous exercise at 60% of VO₂max, and a 5-minute cool-down at 30% of VO₂max.

For the HIIT group, the first week consists of three sessions including a 5-minute warm-up at 30% of VO₂max, 20 minutes of exercise at 60% of VO₂max, and a 5-minute cool-down at 30% of VO₂max. Starting from the second week, interval training will be implemented as follows: 5 sessions of 20 minutes with intervals alternating between 65-80% of VO₂max for 60 seconds and 50% of VO₂max for 120 seconds; 5 sessions of 20 minutes alternating 65-80% of VO₂max for 120 seconds and 50% of VO₂max for 120 seconds; and 5 sessions of 20 minutes alternating 65-80% of VO₂max for 240 seconds and 50% of VO₂max for 180 seconds.

Both groups will be completed a total of 18 sessions over 6 weeks, with training occurring three times per week. Resistance training exercises will be incorporated into the programs in both groups after the second week. Load increments of 5 watts will be applied based on patient tolerance.

Inclusion Criteria:

Patients aged 18-75 years heart failure (HF) NYHA class II-III left ventricular ejection fraction (LVEF) <0.40, BMI between 18-30 kg/m² standard medications at stable doses for at least two weeks prior to enrollment

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Exclusion Criteria:

a history of cardiac implant device placement within the previous 6 weeks a planned cardiac device implantation heart transplantation within the next 12 months acute coronary syndrome within the prior 6 weeks severe valvular or congenital heart disease severe hypertrophic obstructive cardiomyopathy acute myocarditis or pericarditis intracardiac thrombus primary pulmonary hypertension peripartum cardiomyopathy uncontrolled hypertension (systolic blood pressure >200 mmHg and/or diastolic blood pressure >110 mmHg) severe arrhythmias.

The patients will be blinded to group allocation, and the exercise group will be determined through randomization, after which the appropriate program will be administered accordingly.