Iron deficiency (ID) is recognized as an important comorbidity in patients undergoing cardiac surgery; however, it still remains under-diagnosed and under-treated in clinical practice. This study aims at comparing efficacy and the effects on exercise capacity of intravenous ferric carboxymaltose (FCM) versus ferric gluconate (FG) in patients with ID anemia (IDA) resulting from cardiac surgery. We retrospectively analyzed data from our records of in-hospital patients with IDA after cardiac surgery undergoing cardiac rehabilitation. Group I was treated with FG, group II with FCM. Efficacy measures included changes (baseline vs discharge) in hemoglobin (Hb) and in distance traveled at six-minutes walking test (6MWT). Data from 74 in-patients (mean age 67.5±10.4 years, 43% women) were analyzed. At discharge, patients treated with FCM showed higher levels of Hb (11.1±1.2g/dl vs 10.2±1.1 g/dl; p=0.001), greater distance traveled at 6MWT (279.2±108.8 meters vs 236.3±72.7 meters; p=0.048), and lower in-hospital rehabilitation length of stay (20.3±7 vs 25.3±11.7 days; p=0.043) as compared to FG group. At multivariate analysis, the most powerful predictors of Hb increase >1 g/dl at discharge were transferrin levels (p=0.019) and treatment with FCM (p<0.001). FCM replacement therapy and iron serum levels were the most powerful predictors of 6MWT distance improvement (>100 meters) at discharge (p=0.13 and p=0.003, respectively). In patients with IDA following cardiac surgery, intravenous FCM is effective in restoring Hb levels and in improving exercise capacity after cardiac surgery.