<h3>Introduction</h3> The development of left bundle branch block (LBBB) after orthotopic heart transplant is uncommon. We present a case of transient left bundle branch block associated with septal edema after orthotopic heart and lung transplant. <h3>Case Report</h3> A 47-year-old female with hereditary pulmonary arterial hypertension is on 4L oxygen despite the use of sildenafil, macitentan, and intravenous epoprostenol. She had severe right ventricular, right atrial, and pulmonary artery dilation with severe pulmonic and tricuspid insufficiency on echocardiogram (TTE). Right heart catheterization revealed PVR of 10.1 wood units. Patient underwent uncomplicated dual heart and lung transplantation (CBT 225 minutes, DIT 130 minutes, basiliximab induction). Donor was a 40-year-old female with ejection fraction 50%, septal wall (IVS) 1.45 cm, CI 6.6 L/min/m<sup>2</sup>. On post-op day 1 (POD#1) patient was in sinus tachycardia with a new LBBB on electrocardiogram (ECG). QRS interval increased from 94 ms to 154 ms. TTE showed preserved left ventricular function with no wall motion abnormality but significant IVS edema measuring 1.7 cm. Immunosuppression regimen was tacrolimus 1 mg twice daily, mycophenolate mofetil 1 g twice daily, and prednisone 10 mg daily. QRS interval remained stable over the next few days and normalized to 98 ms on POD#5. Repeat TTE showed decrease in IVS thickness to 1.5 cm. Patient had an uneventful remainder of hospital stay and was discharged home two weeks later. Her IVS on TTE three months post-transplant decreased to 1.1 cm and she continues to do well. <h3>Summary</h3> The development of LBBB acutely after orthotopic heart transplant is uncommon and the clinical significance is unknown. We highlight a case of a 47-year-old female who underwent heart and lung transplantation complicated by the acute onset of LBBB due to significant post-operative septal edema. Serial ECGs demonstrated stable QRS interval and spontaneous resolution of LBBB with improvement of septal edema on day 5 after transplant.