First Heart Sounds

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This course will teach you about first heart sound auscultation. Before you take this course you should have finished the Normal Heart Sounds course and feel comfortable with your ability to listen and recognize normal heart sounds.

Using this course

Each lesson in this course includes text describing the heart or lung abnormality and a simulated torso indicating the stethoscope chestpiece location. An audio recording of the sound is provided. Phonocardiograms or waveforms are included with each lesson. These waveforms can be a highly useful aid in learning to recognize heart murmurs. In addition, short videos clips illustrate the heart's motion for each abnormality. These animations indicate the origin of each murmur. Blood flow is also animated. For lung sounds, the source (location) of the sound can be revealed.

After completing a lesson, use the lesson table of contents to navigate to another lesson.

When all lessons have been completed, we recommend using the auscultation practice exercises or quiz. In order to gain a certificate of achievement, please complete the course lessons and practice drill during one session. Most users complete the course's lessons and drill in 30-45 minutes.

Authors and Reviewers

Authors: Jonathan Keroes, MD, Cardiologist (ret.), David Lieberman, Heart Sound Simulation Consultant. Medical review by Dr. Barbara Erickson.

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Lesson #1: First Heart Sound - Loud

Usually, the first heart sound is slightly louder than the second heart sound when heard in the Mitral valve area. In this case the first heart sound is much louder than the second heart sound. This can be produced by a thickened, but still mobile, mitral valve. Look at the anatomy video to see the thickened mitral valve leaflets. A very loud first heart sound can be an indication of mitral stenosis.

Lesson #2: First Heart Sound (Minimally Split)

On occasion the first heart sound can be made up of two separate sounds separated by a very small interval (20-30 milliseconds). The Mitral component (caused by closure of the Mitral valve) comes first and is louder than the Tricuspid component (caused by closure of the Tricuspid valve). A minimally split first heart sound is a normal variation of the first heart sound.

Lesson #3: First Heart Sound (Markedly Split)

If the splitting of the first heart sound is large (about 50 milliseconds), it is an indication of an abnormal condition called Right Bundle Branch Block. The splitting is most clearly heard at the tricuspid area. In the mitral valve area, the mitral component is louder. At 50 milliseconds, the splitting of the first heart sound is clearly audible.

Lesson #4: First Heart Sound - Decreased Intensity

A decreased intensity first heart sound can be produced by various heart abnormalities, such as a viral infection of the heart called a cardiomyopathy. Other conditions include a previous heart attack and decreased thyroid function. The decreased intensity first heart sound is due to a decrease in the vigor of contraction of the left ventricle. See the anatomy video.

Lesson #5: Fourth Heart Sound Plus First Heart Sound

Certain heart sound configurations mimic a split first heart sound. One of these conditions is a fourth sound gallop (S4) plus a first heart sound (S1). Since the S4 occurs just before the S1, it is easy to confuse a S4/S1 with a split S1. An S4 is lower frequency than an S1. To differentiate between a S4/S1 and a split S1, listen carefully to the frequency of the initial sound of the pair. If it is lower in frequency than the second sound, it is an S4. If the two sounds are the same, it is a split S1.

Lesson #6: First Heart Sound plus Aortic Ejection Click

A single first heart sound (S1) followed by an aortic ejection click (AEC) can also mimic a split first heart sound. An AEC follows S1 by 50 milliseconds. An aortic ejection click is caused by thickened aortic valve leaflets. This is commonly seen in a bicuspid aortic valve, a congenital abnormality where someone is born with two aortic valve leaflets instead of the normal three. Listen carefully to the second sound of the pair. If it is an AEC it will have a shorter duration and a higher pitch than the first sound of the pair (S1). The AEC is best heard at the Aortic valve area where splitting of S1 is not heard.

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