Background: Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is a rare congenital cardiac anomaly. The majority of patients die within the first year of life if left untreated. However, a few patients can be asymptomatic and survive into adulthood due to well-developed collateral between the left coronary artery and the dilated right coronary artery. Case presentation: We reported a case of a male who has been having nonspecific symptoms since infancy which were misdiagnosed as symptoms of heart failure. At the age of 18 years old, he presented with a sudden death, and his autopsy revealed ALCAPA syndrome with a dilated right coronary artery. Histopathological studies demonstrated myxoid degeneration of media of the proximal left coronary artery (LCA), right coronary artery (RCA) collaterals, the proximal RCA and the leaflet of mitral valve. In addition, interstitial fibrosis of the papillary muscle of the the mitral valve and leaflet of mitral valve, distal LCA, and in the left ventricle endocardium was observed. Conclusions: Aperiodic diagnosis and follow-up for the cardiovascular system is recommended for similar cases. In addition to the current recommended approaches for ALCAPA treatment, further studies emerge the need for determining reliable, noninvasive diagnostic biomarkers for early screening this congenial anomaly of the heart during infancy to avoid a tragic ending.