Case Presentation: We present the case of a 74-year-old female patient who presented to the emergency department with lower extremity weakness found to have a fixed frequency square wave artifact in all leads of her electrocardiogram (ECG). After troubleshooting, faulty external cardiac monitor leads were identified as the cause of this unique artifact.

Discussion: The ECG is an important diagnostic tool for medical providers. Electrocardiogram artifacts are extremely common, and knowledge of artifacts is necessary to prevent inappropriate interpretation, diagnostic error, and unnecessary workup. Medical providers should have a low threshold for suspicion when ECG findings do not correlate with the patient’s chief complaint or history of present illness. They must also be familiar with the most frequent ECG artifact variants and be prepared to follow a stepwise approach to troubleshoot less frequent variants.