To identify the clinical factors associated with acute rejection (AR) in the first year after heart transplantation (HT), we analysed 112 patients. All patients received OKT3 and standard triple-drug therapy. We analysed the following variables to determine their relationship with AR: age and gender, panel-reactive antibodies, HLA-DR mismatch, use of Sandimmune vs Neoral, diltiazem administration, and cyclosporine levels in week 2 and months 1, 2, and 3 after HT. Fifty-two patients had no AR and 49 had at least one episode. The variables independently associated with absence of AR were diltiazem administration (odds ratio 0.306, confidence limit 0.102-0.921) and cyclosporine level in the first month after HT (odds ratio 0.996, confidence limit 0.992-0.999). Furthermore, a cyclosporine level greater than 362 ng/ml in the first month predicted the absence of AR. In conclusion, a cyclosporine level greater than 362 ng/ml and diltiazem administration in the first month after HT reduce AR during the first year. Both cyclosporine level and diltiazem show a large and independent protective effect.