Mycophenolate mofetil (MMF) is included in the basic immunosuppression regimen in heart transplantation (HTx). Classically, the mycophenolic acid (MPA) concentration has not been considered to provide clinical information.To perform a comparative analysis of MMF dosage and MPA concentration and their effect on post-HTx renal function.Sixty patients underwent HTx between January 2007 and April 2009, and were followed up at 4 scheduled visits in 6 months. The standard MMF dose was 1000 mg/12 h, with adjustment according to clinical criteria. The MPA concentration was determined using an enzyme-multiplied immunoassay (EMIT 2000; Siemens Healthcare Diagnostics Inc, Deerfield, Illinois), without change in dosage. The correlation between mean MMF dosage and MPA concentrations at all visits vs renal function values was analyzed using serum creatinine concentration, creatinine clearance (CrCl; Modification of Diet in Renal Disease), and glomerular filtration rate (GFR; Cockcroft-Gault formula).Mean (SD) patient age was 50 (13) years, and 45 of 60 (75.4%) were men. Pre-HTx values were as follows: creatinine concentration, 1.13 (0.47) mg/dL; CrCl, 81.59 (36.84) mL/min/1.73 m2; and GFR, 77.46 (30.60) mL/min. In the first 6 months post-HTx, significant negative correlations were observed between mean MPA concentration and creatinine concentration (r=.42; P=.001), CrCl (r=-.36; P=.01), and GFR (r=-.45; P=.001). No correlation was observed with mean MMF dosage.There are important differences in the relationship of MPA concentration vs MMF dosage and post-HTx renal function. Although studies with a larger number of patients are needed, treatment guided by MPA concentration seems reliable for evaluation of renal function.