Although several studies have looked at the safety and efficacy of flecainide in the treatment of atrial tachyarrhythmias in native hearts without structural heart disease, its use in transplanted hearts has not been previously reported. To investigate the safety and efficacy of flecainide use for the management of atrial tachyarrhythmias in the immediate post heart transplant population. We retrospectively evaluated patients treated for atrial tachyarrhythmias immediately post heart transplant with flecainide from 5/2010 to 11/2022 at our institution. Clinical variables were examined and patient records screened for time to initiation of flecainide, duration of treatment, subjective and objective efficacy, hospitalization, failure of treatment requiring catheter ablation and mortality while on flecainide. Among 30 patients (87% male, age 58.1 ± 11.2 years), median ejection fraction was 65% (range 50-75%) and median left ventricular wall thickness was 1.0 cm (range 0.7-1.2 cm). The average time to initiation of flecainide was 13.4 (range 5-28 days) post transplantation with a mean treatment duration of 314 ± 539 days. The median flecainide dose was 100 mgs twice daily. Indications for flecainide use were atrial fibrillation 77%, atrial flutter 43%, atrial tachycardia 13%, and supraventricular tachycardia 3%. All patients reported significant symptom reduction on flecainide, with none of the patients experiencing syncope, ventricular tachyarrhythmias, or hospitalization as a consequence of flecainide use or toxicity. Reasons for stopping flecainide were complete resolution of atrial tachyarrhythmias after at least 6 weeks of treatment in 79%, successful catheter ablation 15%, switching to alternative antiarrhythmic drug 3%, and death from PEA arrest in the setting of massive stroke in 3% (1 patient). Flecainide is effective for the treatment of atrial tachyarrhythmias immediately post heart transplantation. While this study suggests safety, larger cohorts are needed to confirm these findings.