Lub-dub…dub? When our heart breaks into a gallop

We’re all familiar with the melodic rhythm of a beating heart. Lub-dub, lub-dub, lub-dub. It’s almost peaceful to be reassured that the trusty little muscle is ever so reliably at work to keep us going (thanks, heart!). If lub-dub is the sound that gives us life, then what happens when we hear lub-dub-dub? A third sound to our heart’s beat is not as uncommon as you might think. So, what does the added dub actually mean? Are we then suddenly destined to be filled with one third more ‘life’? Well, maybe not…

What third heart sound?

If you’ve never heard or felt the rhythm of someone’s heart consist of three beats, that doesn’t mean it isn’t there. Surprisingly, the third heart sound is relatively common – it’s just difficult to hear! The standard lub-dub we all know and love, known as S1 and S2, are of course very easy to detect. The elusive third dub, known as S3, is a very low-frequency vibration, and requires a stethoscope to detect if it is present. If detected, S3 occurs in close succession to S2, creating the rhythm of a gallop. If you’re not so familiar with how four-legged animals run, the rhythm of the word “Kentucky” is another way the lub-dub-dub has been described: “KEN-TU-CKY”, “S1-S2-S3”. It’s no surprise fried chicken is held so dear in people’s hearts after all!

Image credit: Kumar’s edit via Flickr

Quieten down in there!

Apart from the added bonus of being a testament to the living, the sounds of a beating heart clearly have a physiological origin. S1 and S2 are actually the sounds produced when the two pairs of valves within our heart slam shut as blood is pumped through the system. They act as floodgates to the flow of our blood, and ensure there is only flow in the correct direction. Thanks to these valves, our heart is the most efficient it can be – there’s no point in trying to pump blood around the body, if it will just trickle back in the other direction again! The pairs of valves open, allow blood to flow through as the heart muscle contracts and squeezes it out, then slam shut again to prevent backflow. Two pairs of valves at different points in the system create two distinct sounds: lub and dub. The reason S3 is so faint and not always present is because, unlike S1 and S2, it is not the result of the closing of valves. There are a couple of different theories behind the origin of S3, which may depend on the age and health of the person.

When less is more

Unfortunately, S3 is not necessarily something to be sought after. In people over the age of 40, the galloping heart sound can be an indication of heart complications. In this case, the sound results from leaky heart valves. As the closing of the valves produce S1 and S2, S3 follows shortly after as blood regurgitates backward in the wrong direction. This in itself may not be that harmful, but can be an indication of a more severe underlying complication. Doctors may use the presence of a third heart sound to guide their diagnoses, but it’s not something for anyone to worry about personally – you won’t be able to hear it yourself anyway!

But three’s a party!

Before you get all spiteful toward a heart that can gallop, fear not! The third heart sound can also be a sign your heart’s in great shape. S3 may also be the result of the elastic recoil of the heart muscle after it contracts with each beat. A heart with an extra strong and mighty beat will have an extra strong and mighty recoil, which creates the additional ‘dub’. In younger people, especially athletes or pregnant women, this is a common and natural phenomenon, that tends to disappear by middle age (not that you would notice!).

Image credit: Britt-knee via Flickr

So if you’re young, fit and feeling fine, you may even have a third heart sound yourself, without even knowing it. If you’re older and worried a third heart sound might not be a great thing for you, don’t worry – that’s something your heart will tell your doctor about! So you may not ever know whether or not your heart’s a galloper, the most important thing is that it’s running at all!


6 Responses to “Lub-dub…dub? When our heart breaks into a gallop”

  1. Felicity says:

    I never knew about the second “dub”, nor that it could be a perfectly normal sound. So much variation can be brushed over when we generalise things for science/communication, which can be such a shame (even if it is useful).
    Thanks for writing this – your style is engaging and clear!

  2. Marie says:

    Hi Jessica, interesting read. While I had heard of third beats in a heartbeat, I never knew it could be a sign of an extra strong heart with a strong of recoil, that’s reassuring! Thanks for sharing!

  3. Jessica Kamar says:

    Thanks Kimberley, I’m glad you enjoyed reading!

  4. Jessica Kamar says:

    Hi yixiaos1 (sorry, not sure what your first name is!)
    Thanks for your questions! The function of the third sound, and what it is actually produced by, depends on the context of the person. There is no concrete physiological explanation, as there is for S1 and S2. It is generally agreed on that in young age it is an indication of a healthy, high-functioning heart (such as in fit athletes), while in older people it may be an indication of heart failure and a weakening of the valves. Essentially, it is approached on a case by case basis, depending on age, general health status, and what other symptoms the patient may be presenting with. An interesting aspect of physiology that is certainly not black and white.
    I hope this helps!

  5. Kimberley Meyers says:

    A great article, Jessica! I had no idea we could have an extra dub! I liked your tone throughout and you structured your writing well.

  6. yixiaos1 says:

    Sorry if I said anything wrong..But I am not sure what you mean for these subtitles across the blog and somehow they made me feel more confused about the points you made with in the later paragraphs.

    Also, for content, what does the third dub actually do? I only get that the third dub exist during the young age, and might disappear later (??). But for med-age group, the appearance of the third sound might due to the back-flow of the blood between the values. So what is the importance of the third dub??

    However, the lub-dub-dub idea is quite interesting, and very easy to understand when it’s about the pattern of the heatbeat. I also attract by the title as well. Hope you won’t mind my questions..