coronary artery fistula ( caf ) is an unusual coronary artery abnormality , where connection exists between coronary artery and cardiac chamber or another blood vessel . caf originating from the left main trunk and left circumflex artery is very unusual and rarely reported in the literature . we describe a case of giant left main trunk and left circumflex artery fistula to the right ventricle . a 24-year - old male patient presented with complaints of dyspnea and palpitation during exercise . on physical examination , his blood pressure was 120/80 mmhg and pulse rate was 75 bpm . the heart was rhythmic and chest auscultation revealed a continuous murmur of grade 3/6 at the upper left sternal border . transthoracic echocardiography ( tte ) showed enlargement of the left main trunk and left circumflex coronary artery , with a 25-mm inner diameter , diffusely tortuous dilated and drained into the posterior wall of the right ventricle [ figure 1 ] . left anterior descending artery , right coronary artery , and major side branches were normal . the left ventricular systolic function was normal with an ejection fraction of 65% and there were no abnormalities in the regional wall motion and cardiac valves . laboratory investigations were normal . in order to further evaluate the fistula in more detail , a 320-slice dynamic volume ct ( aquilion one , software release v. 4.3 , toshiba medical systems , japan ) angiogram was performed , using 3-dimensional volume - rendered ( vr ) and curved - plain reconstruction ( cpr ) . it demonstrated a large fistula arising from the left main trunk and left circumflex artery emptying to the right ventricle [ figure 2 ] . color - doppler echocardiography revealed enlarged and tortuous of lm and lcx ( white arrows ) origin from ao , abnormal flow from ao passing lm and lcx to rv through a fistula ( red arrow ) . ( ao : aorta , lm : left main trunk , lcx : left circumflex artery , lv : left ventricle , rv : right ventricle , ra : righe atrium , la : left atrium ) contrast - enhanced ct coronary angiogram . 3-dimensional volume - rendered ( vr ) and curved - plain reconstruction ( cpr ) shows origin and course of the fistula . the vessel runs from the left main trunk and left circumflex coronary artery and drained into the posterior wall of the right ventricle through a fistula ( red arrow ) . ( ao : aorta , lm : left main trunk , lcx : left circumflex artery , lv : left ventricle , rv : right ventricle ) congenital caf is caused by a cardiovascular abnormality in embryo period , which accounts for 0.27 - 0.40% of all congenital cardiac defects . acquired caf has been described after surgical procedures , endomyocardial biopsy , trauma , inflammation , atherosclerosis , and collagen vascular disease . caf usually drains into the right chamber , pulmonary artery , pulmonary veins , superior vena cava , inferior vena cava , and coronary sinus . most caf patients are usually asymptomatic and are found incidentally during angiographic evaluation for other cardiac diseases . clinical symptoms of patients with caf are dependent on the size of fistula and the pressure of its terminal chamber . in our patient , the giant caf increases the volume load of the right heart chambers and the pulmonary artery . if the shunt of caf is significant , steal blood phenomenon may occur and cause myocardial ischemia or infarction , which increases risk of infective endocarditis , accelerates atherosclerosis , and even heart failure . generally , tte is an important primary non - invasive tool for diagnosis of coronary artery abnormality and confirmed by coronary angiography . with the cardiac ct technological improvement in recent years , particularly in temporal / spatial resolution and reduced radiation dose , coronary computed tomography angiography ( ccta ) has been a relatively new imaging modality and non - invasive method for assessment of coronary artery disease . ccta not only precisely demonstrate the origin , course , and drainage site of the fistula , but also provides surgical plan for treatment . it is suggested that caf should be treated as soon as possible to avoid the potential risk of complications , no matter whether clinical symptom exists or not . in our case , he experienced no serious cardiac events over half a year of follow - up . in conclusion , the giant left main trunk and left circumflex artery fistula to the right ventricle are rarely seen .