The content published in Cureus is the result of clinical experience and/or research by independent individuals or organizations. Cureus is not responsible for the scientific accuracy or reliability of data or conclusions published herein. All content published within Cureus is intended only for educational, research and reference purposes. Additionally, articles published within Cureus should not be deemed a suitable substitute for the advice of a qualified health care professional. Do not disregard or avoid professional medical advice due to content published within Cureus. Introduction ============ Coronary artery fistula (CAF) refers to an abnormal communications between a coronary artery and any adjacent structure, predominantly cardiac chamber or great vessels \[[@REF1]\]. CAF is a rare congenital anomaly with a prevalence ranging from 0.15%-0.2% \[[@REF2]\]. The overall incidence of CAF in patients with congenital heart disease is 0.4% \[[@REF3]\]. It has been reported that CAF is a rare phenomenon (incidence of 1% of all congenital cardiac defects) with a wide spectrum of clinical manifestations ranging from an incidental finding to a fatal presentation. The most commonly affected site is the right coronary artery (RCA), followed by the left anterior descending (LAD) artery \[[@REF4]\]. In contrast, in our case, the RCA was fed by a fistula originating from the left main coronary artery (LMCA) and it was anastomosed to the right ventricular (RV) wall. We described a rare case of giant CAF originating from the LMCA to RV cardiac walls with a right-sided aortic arch with a bicuspid valve.  Case presentation ================= A 25-year-old male was presented to the emergency department with sudden-onset syncope for the last two days. He had no history of hypertension, diabetes, or coronary artery disease. There were no risk factors for atherosclerosis or vasculitis. Clinical examination revealed mild hypotension with cold and clammy extremities. Blood pressure was 90/60 mm Hg. There was a grade 3/6 continuous cardiac murmur loudest in the cardiac apex with radiation to the right upper parasternal area. Electrocardiography showed normal sinus rhythm, normal axis with no ischemic changes. In addition, chest X-ray was normal. Transthoracic echocardiography demonstrated normal left ventricular function with global hypokinesis of the right ventricle. The right atrium and right ventricle were dilated (right atrial: 36.3 mm, right ventricular: 48 mm), with an estimated RV systolic pressure of 86 mm Hg (Figure [1](#FIG1){ref-type="fig"}). The patient was admitted to the intensive care unit with a diagnosis of non-ST elevation myocardial infarction. Further laboratory investigations were unremarkable. Coronary angiogram showed a right dominant circulation with a giant CAF originating from the left main coronary artery and it was anastomosed to the right ventricular wall, which was also draining into the right atrium (Figure [2](#FIG2){ref-type="fig"}). {#FIG1} {#FIG2} Discussion ========== Coronary artery fistula (CAF) is defined as an anomalous connection between one or more coronary arteries and a cardiac chamber or a great vessel. This connection allows a coronary artery to act as a direct conduit between a coronary artery and a cardiac chamber or great vessel. This congenital condition is rare and estimated to be 0.2%-1% of all congenital heart anomalies and its prevalence is higher in patients with tetralogy of Fallot and single ventricle (2.9%) and those with Alagille syndrome (4%) \[[@REF5]\]. The most common locations of CAF are the right coronary artery, followed by the left anterior descending (LAD) artery \[[@REF6]\]. CAF has also been reported in the right coronary sinus, the left coronary sinus, the right ventricle (RV), the left atrium, and the pulmonary artery \[[@REF7]\]. Coronary artery fistula has diverse clinical manifestations. Although it is usually an incidental finding during coronary angiography, this lesion is increasingly diagnosed with increasing availability of cardiac imaging modalities \[[@REF8]\]. Coronary artery fistulae may be asymptomatic or be complicated by an aneurism, myocardial infarction, myocarditis, endocarditis, stroke, and heart failure due to the steal effect \[[@REF9]\]. In our case, our patient had significant cardiac tamponade with a right-sided aortic arch, which is the least common cardiovascular anatomical variant of aortic arch abnormalities. Coronary angiography, coronary computed tomography (CT) scan, and transthoracic echocardiography are the main imaging modalities used for diagnosis of CAF \[[@REF8],[@REF10]\]. Echocardiography is an essential component of the diagnosis of CAF; however, cardiac CT is a better imaging modality for the demonstration of the exact anatomy and morphology of CAF. It also helps to identify proximal sources of shunt. Moreover, it can also identify the associated anomalous coronary artery and assess proximal source of shunt. In addition, coronary angiography can be useful in detecting CAF during balloon angioplasty or stent implantation for the treatment of coronary stenosis \[[@REF11]\]. Treatment of CAF depends on the hemodynamic significance. In the absence of significant shunt flow, surgical closure is not necessary. Surgery is indicated when the patient develops symptoms such as heart failure, myocardial infarction, and atrial fibrillation \[[@REF5]\]. Conclusions =========== Coronary artery fistulae are rare and unusual coronary anomalies. Clinical manifestations vary significantly due to the size, type of fistulae, and associated cardiac anomalies. Patients with a coronary artery fistula often present with vague complaints like chest pain and atypical chest discomfort with a wide range of clinical manifestations. Therefore, it is important to consider these clinical manifestations in order to achieve a proper diagnosis and prognosis. In our case, this patient presented with a sudden cardiac arrest and syncope without a history of coronary artery disease, valvular disease, hypertension, or diabetes mellitus. In our case, echocardiography revealed significant cardiac tamponade with a right-sided aortic arch. The authors have declared that no competing interests exist. Consent was obtained by all participants in this study