Purpose <p>This study aimed to evaluate the effectiveness of an online educational program designed to improve nurses’ skills in interpreting electrocardiograms (ECGs).</p> Methods <p>This study employed a single-group pretest‒posttest quasiexperimental design. The population consisted of 282 nurses who voluntarily participated in the online ECG education program. The five-hour online ECG education program covered six main topics: normal sinus rhythm and derivations, arrhythmias of sinus origin, arrhythmias of atrial origin, arrhythmias of ventricular origin, blocks, pacemakers, acute coronary syndrome, and myocardial infarction.</p> Results <p>Participants had significantly higher mean posttest scores on the Electrocardiography Knowledge Test (ECG-KT) than did their pretest scores. Specifically, they achieved significantly higher posttest scores in the “normal sinus rhythm and derivations,” “atrial arrhythmias,” and “acute coronary syndrome” subcategories than did their pretest scores. The participants with intensive care certificates demonstrated significantly higher mean pretest and posttest ECG-KT scores than did those without such certificates. Additionally, participants with master’s or Ph.D. degrees had significantly higher mean pretest and posttest ECG-KT scores than those with bachelor’s degrees did.</p> Conclusion <p>The results indicate that the ECG education program enhances nurses’ knowledge and improves their ability to interpret ECGs quickly and accurately. Therefore, universities and hospitals are recommended to offer online ECG education programs to support nurses in developing these essential skills.</p>