Auscultation in Primary Care Third 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 Third Heart Sound Gallop A#31 (lesson# 4) within course number 4. A third heart sound occurs early in diastole. In young people and athletes it is a normal phenomenon. In older individuals it indicates the presence of congestive heart failure.The third heart sound is caused by a sudden deceleration of blood flow into the left ventricle from the left atrium. In the anatomy tab you will see a thin-walled, dilated left ventricle with generalized decreased vigor of contraction.In the presence of a third heart sound (S3) the first heart sound is decreased in intensity while the second heart sound is increased in intensity.The third heart sound is a low frequency sound best heard with the bell of the stethoscope pressed lightly on the skin of the chest.