Auscultation in Primary Care Fourth Heart Sound Gallop Lesson Waveform Anatomy play pause Table of Contents 1First and Second Heart Sounds - Normal and Unsplit 2First and Second Heart Sounds - Reduced Intensity 3Second Heart Sound - Splitting 4Third Heart Sound Gallop 5Fourth Heart Sound Gallop 6Third and Fourth Heart Sound Gallop 7Summation Gallop at 120 beats per minute 8Second Heart Sound - Fixed Splitting 9Mid-Systolic Click 10Mitral Valve Leaflet Prolapse 11Aortic Stenosis (Diamond Shaped Systolic Murmur) 12Aortic Regurgitation (Decrescendo Diastolic Murmur) 13Mitral Regurgitation (pansystolic Murmur) 14Mitral Stenosis (Diastolic Murmur) Quiz This video is an animation of Fourth Heart Sound Gallop A#31 (lesson# 5) within course number 5. The fourth heart sound occurs in late diastole just prior to the first heart sound.The first heart sound is decreased in intensity and the second heart sound is increased in intensity.The fourth heart sound is produced by an increase in stiffness of the left ventricle due to scar tissue formation. This may be a manifestation of coronary heart disease. A fourth heart sound can also be caused by a greatly thickened left ventricular wall such as with essential hypertension or aortic stenosis. This is shown in the anatomy tab.A fourth heart sound is never heard with atrial fibrillation because the contraction of the atria is ineffective in this condition.The fourth heart sound is a low frequency sound best heard with the bell of the stethoscope pressed lightly on the skin of the chest.