Inclusion Criteria:

- Age ≥ 18 years

• Classification as New York Heart Association (NYHA) functional class I-II

• Low surgical risk profile, defined as a EuroSCORE between 0 and 3

• Scheduled for one of the following elective cardiac surgical procedures:

  • Open-heart valve surgery
  • Coronary artery bypass grafting (CABG)
  • Combined valve surgery and CABG
  • Surgical closure of an atrial septal defect (ASD)

• Primary residence in Vienna to ensure the feasibility of in-person assessments and supervised sessions

• Sufficient German language proficiency to participate in assessments and educational components

• Adequate digital literacy to engage with the digital support tools used in the intervention

• Clinical and physical assessment confirming that participation in exercise training is medically safe

Exclusion Criteria:

• Emergency, urgent, or otherwise non-elective cardiac surgery
• Highly complex or specialized surgical procedures (e.g., aortic aneurysm repair, cardiac tumor resections)
• Interventional cardiac procedures (e.g., transcatheter aortic valve implantation [TAVI], MitraClip interventions)
• Neuromotor or physical impairments that might prevent adherence to the study protocol or informed participation
• Contraindications to spiroergometry according to current guidelines:

Absolute contraindications:

• Acute coronary syndrome
• Symptomatic cardiac arrhythmias and/or hemodynamic instability
• Decompensated heart failure
• Acute pulmonary embolism
• Acute endocarditis, myocarditis, or pericarditis
• Febrile infections
• Acute deep vein thrombosis of the lower extremities

Relative contraindications:

• Left main coronary artery stenosis
• Electrolyte imbalances
• Arterial hypertension (>160 mmHg systolic)
• Tachyarrhythmias
• Hypertrophic obstructive cardiomyopathy (HOCM)
• High-grade atrioventricular block
• Anemia
• Physical or psychological impairments