Fourth Heart Sound
The patient's position should be supine.
The fourth heart sound occurs in late diastole, just prior to the first heart sound. The fourth heart sound is a low-frequency sound best heard with a chestpiece bell pressed lightly onto the skin.
The fourth heart sound occurs during the diastolic filling phase, created by increased stiffness of the left ventricle, decreased ventricular compliance, or by increased volume. This may be a manifestation of heart disease. A fourth heart sound is never heard with atrial fibrillation because the contraction of the atria is ineffective in this condition. Review the anatomy video for an example.
The first heart sound is decreased in intensity and the second heart sound is increased in intensity.