BACKGROUND Atrial septal defect (ASD) is the most frequent heart defect observed in adulthood. Although it is usually non-symptomatic, it may result in heart failure, arrhythmic complications, and paradoxical embolism-related morbidity or mortality if the diagnosis is late. OBJECTIVE This study was planned in order to investigate the importance of electrocardiographic findings in the diagnosis of ASD. METHODS Sixty-one patients with a diagnosis of ASD and 66 healthy volunteers without cardiac disease were enrolled in the study. Electrocardiographs (ECG) were performed on all patients to investigate the presence of right bundle branch block (RBBB), incomplete RBBB, defective T wave (DTW), and notch finding in the R wave of inferior derivations (crochetage R wave). ASD types and diameters were determined via transthoracic and transoesophageal echocardiography. RESULTS It was determined that incomplete RBBB (56% vs. 5%), DTW (48% vs. 3%), and R wave crochetage (57% vs. 8%) in inferior derivations were more frequent in ASD patients compared to the control group patients. The specificity of the defined ECG findings in the diagnosis of ASD were 95%, 97%, and 92%, respectively. No correlation was detected between the ASD diameter and incomplete RBBB, whereas significant correlation was observed between the ASD diameter and the presence of crochetage R wave (17.5 ± 4.0 mm in patients with crochetage R wave, and 20.9 ± 8.2 mm in patients without crochetage R wave, p = 0.057). CONCLUSIONS Detection of RBBB, DTW, and crochetage R wave in superficial ECG may contribute to early detection in patients with ASD.