The other important filling sound that may be heard at the apex is the fourth heart sound. It occurs in late diastole, when atrial contraction causes rapid blood flow into the ventricle.
If the ventricle is less compliant than normal, rapid deceleration of blood occurs and causes low frequency vibrations analogous to those occurring with a third heart sound. In the elderly patient, it is not clear if an s4 invariably implies heart disease.
Moving heart S4
This is a graphic example of the heart in a patient with hypertension with a fourth heart sound at the apex. In the animation that follows, we can appreciate that the fourth heart sound is generated during late diastole and it is associated with left atrial contraction.
Volume curve S4
This is a graphic example of an s4 filling sound. By simultaneously viewing the ventricular volume curve, one can appreciate that the fourth sound occurs in late diastole, at the time of rapid flow due to atrial contraction. Let us listen together.