Abstract Body (Do not enter title and authors here): Introduction
High output heart failure (HOHF) due to a post-traumatic aortocaval fistula is a rare entity. This case seeks to explore the presentation as well as complexities of management of these patients.

Case Presentation
A 50-year-old male with a prior right abdominal stab wound requiring exploratory laparotomy 20 years ago presented with worsening dyspnea on exertion and palpitations. Physical examination was remarkable for jugular venous distention, lower extremity edema, and a pulsatile mass in the right abdomen with an audible bruit. A 12-lead ECG showed rapid atrial flutter. A transthoracic echocardiogram (TTE) showed a reduced left ventricular ejection fraction (LVEF) of 30-35%, severely dilated atria and inferior vena cava (IVC) with high velocity flow.

Abdominal computed tomography venogram showed dilation of the IVC up to 8cm and an aortocaval fistula at the level of the right renal vessels, resulting in an atrophic right kidney. Cardiac catheterization was notable for a cardiac output (CO) of 12L/min, cardiac index (CI) of 7L/min/m2 and reduced systemic vascular resistance (SVR). He was managed with beta blockers and diuretics, followed by TEE-guided cardioversion for atrial flutter to restore sinus rhythm. Vascular surgery performed a successful, first of its kind endovascular repair of the abdominal aorta with stenting of the right common iliac artery and placement of a 20mm Amplatzer Septal Occluder device in the right renal artery. He tolerated the procedure well, and post-operative TTE showed a recovered LVEF of 55-60% and CO of 6L/min.

Discussion
HOHF is defined by a CO more than 8L/min or CI more than 4L/min/m2 along with clinical symptoms. Decreased SVR leads to sympathetic activation and stimulation of the renin-angiotensin-aldosterone system, leading to fluid retention, cardiac remodeling, and exacerbation of symptoms. Challenges present in the management of HOHF and the use of vasodilatory agents should be avoided, as they can exacerbate the problem. In our case, limitations were also faced in the use of many traditional HF therapies due to renal dysfunction as a result of the fistula. Therefore, repair was the only viable long-term solution.

Conclusion
This case displays an uncommon etiology of HOHF, emphasizing the need for meticulous evaluation to ensure proper management. Early detection of aortocaval fistulas is crucial to prevent worsening cardiac dysfunction, with symptoms resolving rapidly post-repair.