Background: Physical performance tests are essential for a comprehensive health assessment, and have been described as predictors of disability and muscle mass decline after open chest heart surgery (OHS). We evaluated the association between physical performance tests with clinical outcomes after OHS in younger and older patients. Moreover, the ability of physical performance tests and European System for Cardiac Operative Risk Evaluation (Euroscore II) to predict death was assessed. Methods: Elective OHS patients were evaluated before surgery with handgrip strength (HGS), 30-s Chair-Stand Test (30sCST), and timed up and go test (TUGT). The outcomes were post-surgical complications, total length of stay (LOS), time to walk (TW), time in invasive mechanical ventilation (TIMV), and in-hospital mortality. Data were stratified between patients < 60 (younger) and ≥ 60 years old (older). Results: A total of 166 patients were included in the study (older, n = 89). The only physical test associated with mortality in the adjusted models was HGS in older patients (p = 0.03). Among older patients, both Euroscore II (AUC = 0.77) and HGS (AUC = 0.80) demonstrated good ability to predict death. Combining HGS and Euroscore II did not increase accuracy for mortality prediction (AUC = 0.83). Conclusion: HGS performance was comparable to a well-established surgical risk score in evaluating in-hospital mortality after OHS, only in older patients. Functional testing before OHS could be a tool to improve risk stratification in these patients. Future intervention studies aiming to improve functional capacity before elective OHS can further clarify the impact of physical fitness in surgical recovery.