The presence of complement fixing anti-human leukocyte antigen (HLA) antibodies in the circulation of organ transplant recipients may result in heart allograft rejection. Here, we assessed the clinical impact of pre- and post-transplantation allosensitization on long-term survival of heart allografts. Sequential samples of sera from heart allograft recipients were screened pretransplantation for panel reactive antibodies using the complement-dependent cytotoxicity test. Patients were monitored post-transplantation for donor specific anti-HLA class I and class II antibodies. Kaplan-Meier graft survival plots were generated to analyze the effect of anti-HLA antibodies on transplantation outcomes. Statistical analysis showed that the post-transplantation development of alloantibodies was a significant risk factor that was associated with low long-term survival rates; in contrast, recipients' gender, age, previous transplantations, and degree of HLA matching with the donor had no effect on long-term survival. The presence in pretransplantation sera of antibodies against more than 10% of the HLA reference panel (PRA >10%) was associated with AMR and with a relatively lower rate of graft survival after 1 year but did not affect 10-year survival. The present data underline the importance of monitoring the development of anti-HLA antibodies as a tool for early diagnosis and treatment of AMR.