Normal heart sounds

Normal heart sounds

If you put a stethoscope over the chest, you’ll
usually hear something that sounds like lub dub, lub dub, lub dub, which repeats over
and over again, with each cardiac cycle, or heartbeat. Now, the question is, where does this sound
come from? Normally, blood is constantly moving through
the four chambers of the heart- coming through the veins into the right atrium, going to
the right ventricle, then shooting off via the pulmonary arteries to the lungs and coming
back from the pulmonary veins into the left atrium and the left ventricle, to be pumped
into the aorta. So, in every step, some valves have to open
and others have to close. Valves are just “communicating doors”
that, when open, allow blood to pass through, and when closed, hold blood within a chamber. So, in total, our heart has four valves- two
atrioventricular valves, which separate the atria from the ventricles and are the mitral
valve, on the left side, and the tricuspid valve, on the right side, and two semilunar
valves, which separate the ventricles from the large arteries coming off of them and
are the pulmonary valve, on the right side, and the aortic valve, on the left side. And when these valves are closing, just like
a door slamming shut, they are going to make a sound that is transmitted in the direction
of the blood flow. Now the heart is positioned in such a way
that the sound of the closing of each of these valves is projected onto a small area on the
chest wall. If you place a stethoscope between the second
and third rib, known as the right second intercostal space, just next to the upper border of the
sternum, you’ll hear the aortic valve closing. Then, if you place a stethoscope in the left
second intercostal space, at the left upper sternal border, you can hear the pulmonary
valve closing. Making our way down, between the fourth and
fifth rib, next to the left lower border of the sternum, is where you can best hear the
tricuspid valve closing. Finally, let’s move down to between the
fifth and sixth rib, so in the left fifth intercostal space, near the midclavicular
line. The midclavicular line is the imaginary line
that gets drawn from the midpoint of the left clavicle, or the collarbone, straight down,
and you can find where it intersects with the fifth intercostal space. That’s where the mitral valve closing is
best heard. Now in reality, a lot of these things are
happening at once, like a factory with lots of things happening in parallel. For example, the right and left atria are
both full of blood, and that blood moves through the tricuspid and the mitral valve to get
down into the ventricles. Initially, the blood flows passively into
the ventricles, but near the end when there’s just a bit left, there’s an atrial contraction
that gives the blood an extra hard push to help get it out. This part of the heartbeat, when blood is
filling the relaxed ventricles is called diastole. Now once the ventricles have filled up, both
of the atrioventricular valves snap shut, creating a long, loud sound that sounds a
bit like “lub”. That’s the first heart sound, or S1. And because it’s basically the tricuspid
and mitral valve closing, it’s best heard in the tricuspid valve and mitral valve area. So, at this point, the ventricles are full
of a whole lot of blood and are ready to squeeze it out. And to do that, the aortic valve, on the left
side, and the pulmonic valve, on the right side, quietly open up. Blood flows from the left ventricle into the
aorta and from the right ventricle into the pulmonary arteries. This part of the heartbeat, when blood in
the ventricles are contracted and pushing blood out is called systole. Eventually, the ventricles finish squeezing,
so these two valves close down, making a short, sharp sound that sounds a bit like a “dub”. And this dub is called the second heart sound,
or S2. This is heard loudest in the aortic valve
and pulmonary valve area. During inspiration, though, if you listen
carefully with a stethoscope, this S2 sound actually splits into two separate sounds. That’s because the diaphragm muscle lowers
during inspiration, and that creates negative pressure in the chest to bring in air, and
that negative pressure also brings a bit more venous blood back to the right atrium and
right ventricle. It takes a little bit longer for the right
ventricle to squeeze the extra blood into the pulmonary arteries and it takes a little
bit longer for the pulmonary valve to close. So during inspiration, the closing of the
pulmonary valve is heard slightly later than the aortic valve, and that’s called the
physiologic splitting of the S2. Now after both the aortic and pulmonary valves
have shut down, the atrioventricular valves open again, letting the cycle start all over
again. All right, as a quick recap, heart sounds
are generated as blood flows through the beating heart. There are two normal heart sounds- S1, caused
by the atrioventricular valves closing, at the beginning of systole, and S2, caused by
the aortic and pulmonary valves closing, at the beginning of diastole.

77 thoughts on “Normal heart sounds

  1. It's helpful so much, I'm a big fan 😍 I'm waiting your videos continuously and I hope you make a videos for veterinarian students like me.

  2. Good information ….nice vedeo….i request u to make video on the amenorrhoea,crptomenorrhoea, dysmenorrhoea,metrorrhagia,menorrhagia with clinical and sing& symptoms ,diagnosis…pathalogy and physiology…..pls make update this

  3. This video was So frustrating because I stole my dad's old stethoscope to try all this stuff to figure out it's broken

  4. Why do we hear tricuspid valve closing on the Left wherein it supposed to be more audible on the Right side? Can someone enlighten me about that please, I'm quite confuse on that part.🙊

  5. Hi! Ummm around minute 2:00, aren't the aortic and pulmonary valves in the opposite sides? Aortic valve is in the left intercostal and pulmonary should be on the right.

  6. It's not Lub Dub,
    It's Rab Rab
    Which means that the heart is continuously remembering ALLAH, so it's sounding like Rab (My Lord) Rab (My Lord).

  7. 0:56 arrows are on the wrong side of the valves …. That might just be an "illustrative" move, but it's pretty misleading in context and probably not a great way to educate if you immediately have to teach the opposite when you get to the functional bits next.

  8. The closing of the valves themselves does NOT create the hearttones. It’s the turbulence of the blood that is reponsible for these sounds as a RESULT of the shutting of the valves.

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