Mobilisation is recommended following cardiac surgery, but much less is known about its effects on physiological parameters. This study aimed to determine the effect of mobilisation on cardiorespiratory physiological parameters, and to establish the relationship between physiological parameters and physical function following cardiac surgery. Participants requiring physiotherapy following cardiac surgery were recruited. Mobilisation involved ground-based walking, while physical function was assessed using the short physical performance battery (SPPB) test. During both procedures, physiological measures of heart rate (HR), respiratory rate (RR) and percutaneous oxygen saturation (SpO2) were periodically recorded. Participant perception of breathlessness and perceived exertion were recorded pre and post mobilisation and the SPPB test. Forty-five participants (mean [SD] age 69 years) completed the study. HR (mean difference 10[95% CI 8 to 12] bpm) and RR (13[10 to 17] br/min) significantly increased following mobilisation, while SpO2 significantly decreased (baseline median [IQR] 95% [95%–97%] vs nadir 94% [91% to 96%], p < 0.002). There was a significant increase in dyspnoea and perceived exertion (both p < 0.001). There was a moderate relationship between total SPPB score and SpO2 during mobilisation (rs=0.45). Mobilisation following cardiac surgery increases exertion and dyspnoea and alters physiological parameters. Greater physical function is linked to maintaining a higher oxygen saturation during mobilisation.