Electrocardiography (ECG) is one of the most essential diagnostic tools in modern medicine, enabling clinicians to evaluate the electrical activity of the heart in real time. It plays a critical role in diagnosing acute cardiac conditions, monitoring patients in critical care, and supporting decision-making in emergency and remote settings. Although the 12-lead ECG is considered the gold standard for diagnosis, 5-lead and 3-lead ECG systems are equally important in clinical workflows. Each configuration is designed with a specific purpose, balancing diagnostic capability, ease of use, portability, and speed. Understanding how these systems differ—and where they are best applied—is essential for...