Overreliance on technology can open the door to a myriad of errors. This three-part illustrated article series provides insights for practitioners to recognize when computerized readings of electrocardiograms (ECGs) are wrong, to reduce misdiagnosis. Part 1 focuses on common interpretation software errors and false reporting of myocardial infarction, Part 2 looks at software errors that ironically helped to identify a correct diagnosis, and Part 3 highlights software errors that are crucial to catch in order to protect patients from serious harm.