What test is used to evaluate the electrical activity of the heart?

The test used to evaluate the electrical activity of the heart is the electrocardiogram (ECG). This test records the electrical signals that trigger each heartbeat, providing insight into the heart's rhythm, the size of the heart chambers, and any areas of damage or distress. The ECG produces a visual representation of these electrical impulses, known as a waveform, which allows healthcare providers to detect various cardiac conditions such as arrhythmias, ischemia, and prior heart attacks.

In contrast, the other tests listed serve different purposes. X-rays provide images of the heart and surrounding structures to assess physical conditions but do not measure electrical activity. An echocardiogram utilizes sound waves to create images of the heart's structure and can assess pumping function and valve performance, but it does not evaluate electrical impulses. Cardiac MRI uses magnetic fields and radio waves to produce detailed images of the heart’s anatomy and blood flow, again not focusing on electrical activity. Thus, the electrocardiogram is specifically designed for assessing the electrical aspects of heart function, making it the correct choice.