Background: Transplant patients are known to be at increased risk of developing de novo malignancies (DNM). As heart transplant survival has increased, DNM represent an obstacle to further improving survival. We sought to examine the incidence, risk factors, and prognostic factors of post-transplant DNM. Methods: We studied adult heart transplant recipients from the Organ Procurement and Transplantation Network database (1987-2018). Kaplan-Meier survival analysis was performed to determine annual probabilities of developing DNM, excluding squamous and basal cell carcinoma. Rates were compared to the general population in the Surveillance, Epidemiology, and End Results database. Cox proportional hazards regression was performed to calculate hazard ratios for risk factors of DNM development, all-cause, and cancer-specific mortality. Results: Over median follow-up of 6.9 years, 18% of the 49,361 patients developed DNM, which correlated with an incidence rate 3.8 times that of the general population. The most common malignancies were lung, post-transplant lymphoproliferative disorder, and prostate. Risk was most increased for female genital, tongue/throat, and renal cancers. Male gender, older age, smoking history, and impaired renal function were risk factors for developing DNM, whereas the use of MMF for immunosuppression was protective. Cigarette use, increasing age, the use of ATG for induction and calcineurin inhibitors for maintenance were risk factors for cancer-specific mortality. The development of a DNM increased the risk of death by 40% (p<0.001). Conclusions: Heart transplant patients are at increased risk of malignancy post-transplant, particularly rare cancers. Strict cancer surveillance and attention to immunosuppressive regimens are critical for further prolonging post-transplant survival.