Early Rehabilitation in Patients Following Major Cardiac Surgery: Changes in Functional Capacity and Energy Efficiency in Walking and ADLs.

The main objective of this clinical trial is to evaluate exercise capacity before and after an inpatient or outpatient rehabilitation program in patients following major cardiac surgery. Secondary objectives assess baseline levels and changes post-rehabilitation in: * Motor performance and energy efficiency during activities of daily living (ADLs). * Energy efficiency during walking (constant-load treadmill test). * Muscle strength and physical performance via the Short Physical Performance Battery (SPPB) and Five-Times Sit-to-Stand Test (5STS). * Quality of life via the EuroQol questionnaire. Study Design: this 18-month, multi-center study involves several Maugeri Centres in Italy and a total of 60 patients. Participants undergo two assessment sessions (baseline and post-rehabilitation). The prescribed rehabilitation program remains strictly within routine clinical practice and will not be altered. Measurement Device (COSMED K5): selected tests require wearing the CE-marked COSMED K5 portable metabolic analyzer. The system comprises a face mask and a lightweight backpack housing the gas analyzer. By measuring breath-by-breath gas exchange (VO2 and VCO2) alongside heart rate, respiratory rate, and blood pressure, the device precisely quantifies physiological responses to exercise. This data will help optimize recovery tracking and inform future personalized rehabilitation protocols. Evaluations and Tests conducted at baseline and completion of the rehabilitation program: * Six-Minute Walk Test (6MWT): Standard 6-minute walk along a 30-meter course, as required by Italian Ministry of Health guidelines. * Constant-Load Treadmill Test: 6 minutes of walking at constant speed and incline using the K5 metabolic analyzer. * Oxygen Kinetics Test (Cycle Ergometer): Performed in eligible patients based on initial 6MWT performance. Consists of alternating 6-minute workloads (15 W and 35 W sequence: 15-35-15-35-15-35 W) while wearing the K5 analyzer. * GLITTRE ADL-Test: Simulates physical demands of daily living (walking, stairs, carrying weights) while using the K5 analyzer. * Short Physical Performance Battery (SPPB): Standard battery evaluating static balance, 4-meter gait speed, and 5-times sit-to-stand performance. * EuroQol Questionnaire: Brief self-reported quality-of-life assessment. Safety \& Risk Profile: this low-intervention study poses no additional risk beyond routine cardiac rehabilitation procedures (such as transfers, postural changes, and breathing exercises).

Inclusion Criteria: Patients admitted to the Cardiac Rehabilitation Unit at each participating Maugeri Institute who meet all of the following criteria may be enrolled consecutively: * Major cardiac surgery (coronary artery bypass grafting, valve surgery, or combined cardiac surgery) as the index event for the current cardiac rehabilitation episode; * Signed informed consent; * Participation in a complete, structured cardiac rehabilitation program (inpatient or outpatient); * Age greater than 18 and less than 85 years (patients who have not reached their 86th birthday at the time of signing the informed consent form are considered eligible); * Ability to ambulate independently. Exclusion Criteria: * Refusal to participate, including withdrawal of previously given consent; * Concomitant acute neurological and/or orthopedic conditions that affect, impair, or alter walking ability; * Overt cognitive impairment (severe impairment assessed via the Short Portable Mental Status Questionnaire \[SPMSQ\]) and/or diagnosed psychiatric disorders or psychiatric pharmacological treatment; * Clinical instability and/or medical contraindications (hemodynamic instability: SBP \170 mmHg; DBP \>100 mmHg; HR \130 bpm; SpO₂ \