Background. The exact time point at which the first endomyocardial biopsy could be safely performed after the heart transplantation has not been systematically studied. In an attempt to determine this time point in our population, the number and severity of acute rejection episodes in the first eight weeks after the heart transplantation were assessed in 91 patients who underwent the procedure at St Paul’s Hospital, Vancouver between September 1996 and December 2002. Methods and Results. For the purpose of our analysis, acute rejection was defined as the grade ≥2 according the International Society for Heart and Lung Transplantation (ISHLT). Three hundred and sixty two endomyocardial biopsies were performed in 87 patients surviving to the first biopsy from one to eight weeks after the heart transplantation. In 85 patients who received induction immunosuppressive therapy, 13 episodes of acute rejection were identified. In two patients who did not receive the induction therapy, three episodes of acute rejection occurred. Acute rejection grade ISHLT 3 was found in 2 patients who did not receive induction therapy and in three patients who did. ISHLT grade 4 rejection occurred at weeks 5 and 7 in two patients who received induction therapy. Only one patient who received induction therapy had acute rejection within the first three weeks after the heart transplantation. Conclusions. Our analysis reveals that the frequency of acute rejection within the first eight weeks after the heart transplantation using induction therapy is low in this cohort, suggesting that the first routine endomyocardial biopsy could be delayed until the week four post-transplant.

        Key words: heart transplantation, endomyocardial biopsy.