- The Electrocardiogram (ECG) is the primary diagnostic test used to record the heart's electrical impulses.
- It provides a graphical representation of the heart’s electrical activity by measuring the timing and strength of signals as they travel through the heart muscle.
- This allows the identification of arrhythmias, myocardial ischemia, infarction, and conduction abnormalities.
- Unlike imaging modalities, the ECG specifically focuses on the electrophysiological function, making it essential for initial cardiac assessment.
- Other tests like echocardiography and cardiac MRI evaluate structural and functional aspects but do not directly record electrical impulses.

Reference: Davidson’s Principles and Practice of Medicine, 23rd Edition, Chapter: Diseases of the Heart and Circulation, Page 358.