A close association between human herpesvirus-8 (HHV-8) and Kaposi's sarcoma (KS) has been shown in transplant recipients, but donor-to-recipient transmission of HHV-8 is uncommon. Herein we report a case of a heart transplant recipient who had a fatal visceral KS in association with HHV-8 seroconversion at 18 months after transplantation with a donor having positive serology discovered after transplantation.