What is a key preparation for patients undergoing an ECG?

Patients undergoing an ECG should indeed lie still and breathe normally during the test. This is crucial because any movement can interfere with the electrical signals being measured, leading to inaccurate results. Additionally, normal breathing helps ensure that the heart's rhythm can be captured accurately without undue stress or artificial changes caused by the patient’s physical state.

While factors such as the duration of the procedure or the potential for discomfort can play a role in a patient's experience, they do not directly impact the accuracy of the ECG like remaining still and calm does. Furthermore, while talking might distract the patient, the primary need is for stillness to ensure that the electrical activity of the heart is captured effectively. Therefore, the emphasis on lying still and maintaining a normal breathing pattern is the most significant preparation for this test.