The study sought to determine coronary artery diameter in congenital coronary-cameral fistula (cCCF), factors associated with coronary artery aneurysm, coronary artery changes after fistula closure, and computed tomographic (CT) findings after treatment. We retrospectively reviewed CT findings of the cCCF for origins, terminations, fistula length, complexities, and Sakakibara classification. Coronary artery diameter was expressed as coronary artery Z score. Fistula features associated with coronary artery aneurysm were analyzed. Post-fistula closures were analyzed for coronary artery dilatation, coronary thrombosis, complete fistula closure, and fistula thrombosis. Twenty-five patients (median age 33months, interquartile range, IQR 25-48) were included. Coronary feeders and terminations were frequently right coronary artery (48%) and right ventricle (56%), respectively. Fistula aneurysm occurred in 52% of cases. Mean coronary artery Z score was 13.03 ± 6.36 with a high incidence of giant coronary artery aneurysm (68%). We found no statistically significant risk factors associated with coronary artery aneurysm (p value range 0.075-0.370). Median duration of the follow-up CT after closure of the fistulas was 6.4months (IQR 5.0-8.7). Coronary artery Z score significantly decreased by 0.82 (IQR 0.28-1.35), p = 0.006 and coronary thrombosis occurred in 23% of cases during follow-up. Large coronary aneurysm is common in cCCF. No characteristic feature of the fistula influencing coronary artery aneurysm is identified. There is a diminution in coronary artery Z score after fistula closure. Coronary thrombosis is a major complication after treatment.