For 6 years after heart transplantation, a 23-year old female recipient had been treated with immunosuppressants including tacrolimus and mycophenolate mofetil (MMF), without any major rejection or graft dysfunction. She unexpectedly became pregnant for the first time, and we converted MMF to azathioprine (AZA), but she soon experienced a spontaneous abortion. After careful counseling under the continuation of AZA, she became pregnant again 3 months after the abortion. We closely monitored the concentration of immunosuppressive agents, cardiac function, fetal condition, and serological assay including human leukocyte antigen (HLA) sensitization, and she eventually delivered a normal male infant at 38 weeks gestation without any complications. AZA was converted to MMF soon after the delivery. There have been no complications in either the patient or infant after the delivery.Because pregnancy itself involves a risk of cardiac graft rejection in the recipient as well as fetal complications, it is important to educate HTx recipients about planned pregnancy and to conduct careful follow-up after pregnancy.