Normal Heart Sounds

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This course will teach you about auscultation of normal heart sounds including split and unsplit second heart sounds heard at various heart rates and auscultation points.

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 and Second Heart Sounds - Normal and Unsplit

This is a normal first and second heart sound at 60 beats per minute. You are auscultating at the Mitral valve area (Apex). The first heart sound has slightly greater intensity than the second heart sound.
  • The first heart sound is produced by the closing of the mitral and tricuspid valve leaflets.
  • The second heart sound is produced by the closing of the aortic and pulmonic valve leaflets.
  • The second heart sound is unsplit when the subject is holding his or her breath at peak expiration.

Lesson #2: First Heart Sound (Minimal 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: Second Heart Sound - Physiologically Split #1

During normal breathing, the timing between the aortic and pulmonic components of the second heart sound varies. This causes the second heart sound to be split. Maximum splitting occurs at peak inspiration. In the example you are hearing the splitting of the second heart sound is 60 milliseconds at peak inspiration and zero splitting at peak expiration.

Lesson #4: Third Heart Sound - Physiologic

The third heart sound is heard early in diastole. Along with the first and second heart sounds, this extra sound creates a gallop cadence and sounds like "Kentucky." In this auscultation example the second heart sound is unsplit to make it easier for you to distinguish the third heart sound. The third heart sound is very low frequency (between 25Hz and 50Hz). Listen with the bell of the stethoscope at the cardiac apex. Asking the patient to lie on his left side will frequently increase the intensity of the third heart sound. A third heart sound is heard on occasion in normal individuals with no cardiac pathology.

Lesson #5: Innocent Murmur

This is an example of an innocent murmur. This type of murmur is seen with non-cardiac conditions such as pregnancy, hyperthyroidism, exercise and anemia. When these are treated appropriately, the systolic murmur disappears. The murmur is heard in early systole, is of short duration and has a frequency range of 120Hz to 250Hz. It is best auscultated in the pulmonic area and increases in intensity with inspiration. It can be heard with either the bell or diaphragm. In this example S1 and S2 are normal. Diastole is silent. The short duration and mid-range frequency characterize an innocent murmur.

Lesson #6: Exercise - Heart Rate 120

Exercise increases heart action. This increases the heart rate and the intensity of the first heart sound. At 120 beats per minute the durations of systole and diastole are about equal. Other conditions, such as stress, elevated temperature and hyperthyroidism can also increase the intensity of the first heart sound. When these conditions are alleviated, the first heart sound returns to normal. The heart sounds are best heard using the diaphragm of the stethoscope.

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