What does an electrocardiogram primarily show about the heart?

An electrocardiogram (ECG or EKG) primarily shows the electrical impulses moving through the heart. This technique captures the electrical activity that prompts the heart to contract and pump blood. The ECG records the timing and strength of these electrical signals as they progress through the heart’s conduction system, allowing for the analysis of heart rhythms and the identification of various cardiac conditions.

While other recording methods might provide insights into the mechanics of heart movement or its size, the ECG is specifically designed to track the electrical impulses. The interpretation of these impulses can highlight any irregularities in heart rhythm, signs of ischemia, or structural issues that may affect electrical conduction. Therefore, option B is the most accurate reflection of what an ECG primarily shows about the heart.