To review the evidence about inspiratory muscle training (IMT) in patients in postoperative of cardiac surgery. We conducted this systematic review used the databases Ovid, LILACS, CINAHL, PubMed, PEDro, and CENTRAL. Randomized clinical trials that addressed IMT after cardiac surgery were selected. The outcomes assessed were maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), tidal volume (TV), peak expiratory flow (PEF), functional capacity (6-minute walk test) and length of hospital stay. The mean difference between groups and the respective 95% confidence interval (CI) were calculated and used to quantify the effect of continuous outcomes. Seven studies were selected. The IMT was superior to the control over MIP 15.77 cmH2O (95% CI, 5.95-25.49), MEP 15.87 cmH2O (95% CI, 1.16-30.58), PEF 40.98 L/min (95% CI, 4.64-77.32), TV 184.75 mL (95% CI, 19.72-349.77), hospital stay -1.25 days (95% CI, -1.77 to -0.72), but without impact on functional capacity 29.93 m (95% CI, -27.59 to 87.45). Based on the results presented, IMT was beneficial as a form of treatment for patients after cardiac surgery.