Objective: To evaluate the effect of early use of a cycle ergometer, compared to a standard care protocol, in postoperatory in-hospital mobility following cardiac surgery. Design: A randomized controlled trial. Setting: Tertiary hospital in Salvador, Bahia, Brazil. Subjects: Patients submitted to elective cardiac surgery (valvular or coronary bypass surgery by sternotomy). Intervention: Patients were randomly allocated in two groups: (1) cycle ergometer training group (10-minute session) and (2) control group submitted standard physiotherapy protocol (10-minute session). Training was provided twice a day, immediately following extubation and until patient was discharged from the intensive care. Main measures: The primary outcome was the difference in the total number of steps recorded on the pedometer over three days. Secondary outcomes were mobility in different subgroups and the reasons that prevented individuals from walking during early cardiac rehabilitation. Results: A total of 228 participants completed the study. No significant difference was found in the total number of steps between the groups after intervention: 2183 (range: 1729–2772) in the intervention group versus 2006 (1517–2657) in the control group ( P = 0.167). However, self-reports indicated better motivation in the intervention group ( P = 0.044). No adverse events occurred during the study. Conclusion: As a strategy for early mobilization following cardiac surgery, the use of a cycle ergometer failed to increase independent physical activity compared to a standard care protocol. Nevertheless, it was safe and could be an alternative to make rehabilitation more attractive and motivational for this patient population.