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Thyroid UK
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High T4 and low heart rate? Any ideas?

Started to feel a little worried today, my t4 has been high for months and they were going to start treatment but my heart rate is 45 which they say is unusual for overactive. Basically they have no idea what is causing this. I am feeling the cold, not the heat and i have put a little bit of weight on which again is the opposite of what should happen with an overactive thyroid.

I do run a bit and generally quiet active but I do not feel fit enough to have an athletic heart rate of 45!

Any ideas welcomed.

8 Replies

Hi littlemissthyroid. Have they tested your antibodies?


Everything normal apart from T4


I know people diagnosed with Hashimoto's can sometimes wibble wobble from hypo to hyper. I was wondering if that is what is happening to you. Just as well you didn't start treatment for hyperactive thyroid. How are you feeling?


Did they test t3? I had a similar heart rate, sometimes dropping below 40, when I was on levothyroxine. Since switching to t3 only, albeit a rather large dose, my heart rate is a healthy 60ish and I'm not cold all the time. My heart also used to miss beats which concerned 3 cardiologists who couldn't find anything physically wrong with my heart. Seems to have been a t3/reverse t3 issue in my case.

Just a thought :)

Carolyn x

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Thanks for replies - I feel terrible tbh. Can't sit still or concentrate but worn out at the same time. My memory is terrible. Hair is brittle, skin has outbreaks all the time. Hungry all the time - don't seem to be able to feel full anymore. Can be a little up and down with my moods, snap quickly some days.

I had a scan and they said thyroid was normal size and no growths. I went to the doctors last year because my hands and feet were going numb and they tested my bloods. They said this is raynauds and not related to the overactive thyroid that has been picked up.

Some days I run a 4 miles, other days I can't catch my breath and feel so exhausted I cannot continue. I am very worried about my heart rate, its scared me.

T3 is normal.


You need to test serum iron, ferritin, folate, vitamin b12, vitamin D and cortisol. The b12 in particular could be the cause of the numbness but the others need investigating too. Ask for your last FBC results too as these can sometimes highlight what is going on. For example, a high MCV can indicate low b12 that had been an issue for a while. This happened with me. B12 treated and numbness is much better. Still get rReynauds when cold though.

B12 or iron deficiency could also explain your other symptoms including the hyper symptoms combined with the hypo symptoms.

I agree it is very unusual to have such a low heat rate with hyperthyroidism. Very perplexing :(

I hope you find the answer soon.

Carolyn x


I know cortisol was on the tests requested today but not sure about the others you mentioned. Will have to ask tomorrow.



Saw the consultant and got my results back yesterday. All bloods normal including T4. If I get them done in one hospital they are high and if i get them done in another town they are normal. I have no idea what is going on.


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