The fourth heart sound followed by a first sound must be differentiated from a split first sound. The question usually arises when listening at the apex.

It is best to place the patient in the left lateral decubitus position to move the left ventricular apex closer to the chest wall.

Next, palpate the chest wall at the apex to identify the left ventricular impulse. If you feel a presystolic movement just before the systolic left ventricular impulse, the question is settled, as the presystolic impulse is the equivalent of an audible fourth heart sound.