Thyroid cancer and heart problems

Hi. I posted this topic last June -
The relationship of the thyroid and heart.
I have learned that an active thyroid works in concert with your body. The rx does not.
I have not had your issues. I think if you are in the care of a cardiologist, that would be a good plan. Take care.

@kmlnj Thank you so much for your kind reply. It truly means a lot to me.
To be honest, this has been a very difficult journey, especially over the last few days. My heart rate has been getting so high that even simple everyday activities have become difficult for me. Things like taking a shower or doing basic tasks can leave me feeling exhausted and worried.
I have an appointment with my cardiologist this Thursday, and I'm hoping we can look into my tachycardia, palpitations, and irregular heartbeats more closely and find a solution that will help me feel like myself again.
Thank you again for taking the time to respond and for your support. I'm really glad I found this community. It already makes me feel less alone, and it's comforting to be able to share our experiences, thoughts, and feelings with people who truly understand what we're going through.
I look forward to staying in touch with you all. Wishing everyone good health and all the best. ❤️

Hi,
You are definitely not alone with this type of reaction while trying to get regulated on medication. I had a large nodule but did not have any issues with the functioning of my thyroid, until the last FNA. I had a FNA to see if I would be a candidate for Radiofrequency Ablation, however I did not qualify due to a high probability of Hurthle Cell Carcinoma. Shortly after this FNA, I started exhibiting signs of thyroid disease. The nodule had to be removed so in 2022 I had a partial thyroidectomy and I was diagnosed with Hurthle cell carcinoma.

I have had a lot of difficulty getting regulated on thyroid medications. It continues to amaze me, how medication changes or small changes in dosages, can cause or alleviate issues. After surgery I was told it is best to try and suppress the TSH and minimize the risk of regrowth of cancer, however as time went on, we (the Endocrinologist and I) discovered that keeping my TSH very, very low gave me too many side effects. After many changes in medications and dosages and extreme side effects, my doctor looked at my TSH and T4 levels before I had surgery and said we could have my TSH a little higher (still very low) and try to get closer to the levels I had before surgery. This seemed to help a lot.

Although I started with very high doses of medications, my dose is currently extremely low, 13mcg of Tirosint every other day. Although I am still dealing with side effects, they are greatly reduced. Since I have half a thyroid and it is functioning, the doctor has had me stop my medication to see if the side effects change and they always have.

If I was going to offer any advice, I would share that the numbers in your blood work is only one part of the equation…..how you feel is the other part. It is always important to have a doctor who listens to the side effects and does not just look at the numbers in your blood tests. My blood levels were often in the “normal range, “ however my side effects were extreme (leg cramps so bad that I thought I was having a stroke, headaches, nausea, weakness, extreme hip, back and knee pain, stiff and swollen joints in the hands, trigger fingers, sweating like I was overheated and then freezing, weight gain, dizzy, insomnia, feeling “out of it,” etc.

I feel much better on the lower doses even though I am still dealing with some side effects and we have not found the stable dose yet. However, things have improved. DEFINITELY, keep a symptom log. Certain medications/dosages brought out specific side effects so having the log, helped. One very good thing is that medication changes can often be felt immediately so you can get relief. To measure the dose in your blood it takes at least 6 weeks, however the side effects changes are often felt immediately.

Your side effects, sound like they might be directly related to medication and/or dose, so I tend to think your doctor will be able to work with you to make adjustments so you feel better. Good Luck.

@koh Hello! Thank you so much for your reply. It was incredibly helpful, and I really appreciate you taking the time to share your experience with me.
Reading your comment made me realize how many similarities there are between our experiences. I have also been dealing with symptoms such as pain in almost all of my joints. Last year, the pain became so severe that I ended up having MRI scans of my hips and my left shoulder because it was hurting so much. The MRI showed tendinitis and even a tendon tear, and to this day I have no idea how that happened.
I also experience swelling in my fingers from time to time, to the point where I sometimes couldn't even wear my rings comfortably. I mentioned these symptoms to several doctors, but none of them believed they could be related to my high dose of levothyroxine. After reading your comment, I started wondering if my symptoms could actually be connected as well.
Another thing I've struggled with is weight gain. Since my thyroidectomy, I have gained about 25 kg (55 lbs). My doctors were surprised because they kept telling me that, with such a high dose of thyroid hormone, I should actually be losing weight, not gaining it. It was very discouraging because I felt like no one could explain what was happening to me.
After reading your story, I honestly feel that I may be in a very similar situation. It gives me hope to know that I'm not the only one who has experienced this.
I have recently started reducing my levothyroxine dose little by little, and I truly hope that as my body adjusts, these symptoms will gradually improve and I can finally start feeling like myself again.
Thank you again for sharing your experience. It has given me hope and made me feel much less alone. Wishing you all the best on your journey. ❤️

@amaliaspyr One note about the joint pain, I was in PT for the hip/back and knee pain when I went back on medication and it improved drastically. The PT thought it was medication related and when it improved it showed that he was right. When my medication was reduced again the hip pain returned…its like a bursitis.
There is one other area that might be worth asking about and thats the T3. From what I have read and inquired about if T3 can’t manage the amount of T4 in the system it can result in side effects….the T3 processes the T4. If you increase T4 and the T3 can’t process it, it can cause side effects. The usual route for managing thyroid is for medication for T4, however if you are one of those people who do not have enough T3 to process the dose, it can cause side effects. (I don’t think I explained it well but it’s something like T4 is is the medication you need and T3 gets the medication into the cells.) The use of T3 has a lot of associated concerns so doctors prefer to use T4 medications. Good luck

Hi, Amaliaspyr,
I am sorry you are going through all of this and I hope you can get it figured out and get to feeling better, really soon.
I have experienced tachycardia (over 200bpm on average), palpitations and irregular beats, since my recent total thyroidectomy in May (2026). But, I am a bit different because I was born with Supra Ventricular Tachycardia (SVT), which causes high heart rate and what feels like palpitations, so I already have a cardiologist. I had never taken medication for the high heart rate, prior to my thyroidectomy, because the times when my heart rate would get over 200bpm, I could get it back down within a few minutes by using a vasovagal maneuver. However, after my thyroidectomy and getting on levothyroxine 100mcg, it started happening approximately 15 + times a day and I could not easily get it back down with the vasovagal maneuver. I was miserable and exhausted because of it. I had a feeling it was the medication, so I contacted my surgeon and asked if he thought it could be the medication. He lowered my dose of levothyroxine to 88mcg, to see if the symptoms would improve. After, a couple of days, my heart rate was much more normal but would still get really high, a 3-5 times a day. That's better than it happening 15 times a day, but it was still quite bothersome. So, I contacted my cardiologist and he suggested that I begin taking Flecanide 50mg, daily, up to 2 times per day. I have only had to take it once a day and it has helped tremendously. Now, my heart rate only gets up on occasion but it does not last very long. So, I believe the Flecanide is doing its job. Hoping your appt. with the cardiologist was beneficial and you soon can at least get rid of the heart issues.
I don't know if this helps, but I wanted to share what worked for me in hopes that it may help you.
God bless and I will be praying for you.

@anniefannie22 Hi Annie,
Thank you so much for your reply. It was incredibly helpful, and I truly appreciate you taking the time to share your experience with me.
I'm also really happy that I finally found someone who has symptoms so similar to mine. It honestly makes me feel less alone. I'm very sorry to hear about everything you've been through with your health as well, and I sincerely hope you're doing well and continuing to feel better.
After my appointment with the cardiologist, he told me that my resting heart rate was 112 bpm. So whenever I was moving around, it was definitely going up to around 130–140 bpm or even higher. He diagnosed me with tachycardia and told me that I needed to start treatment.
It's been less than a week since I started taking Emconcor 2.5 mg—one tablet in the morning and one in the evening. Thankfully, my heart rate has already dropped quite a bit. It's now usually between 60 and 70 bpm, and the highest I've seen is around 80 bpm. I finally feel like I can do simple things again, like going for a walk or even taking a shower by myself. It's definitely been a huge relief.
Of course, I still feel a little strange sometimes because I had gotten so used to having such a high heart rate, and now it has suddenly become much lower. But overall, I already feel much better than I did before, and I really hope things continue to improve from here.
Thank you so much for all your advice, your kindness, and especially for keeping me in your prayers. It truly means a lot to me.
Also, if you'd be interested, I'd love for us to exchange social media so we can stay in touch more easily and continue sharing our experiences. It would make me very happy.
Thank you again for everything. Wishing you all the best, and I hope you continue to recover and stay healthy.