Missed heartbeats on letrozole

I had a mastectomy in January and have been prescribed letrozole since December
About 2 weeks ago I developed an uneven heartbeat like I missed a beat and then a thud and it went back to normal
I rang me BC nurse on Wednesday who advised me to see my GP
I have read that letrozole can cause these ectopic beats but mine was occurring all the time with occasional few hours when it felt normal. No pain or breathlessness but very worrying
I saw my GP on Thursday who was kind and reassuring and arranged anECG, blood tests and 24 hour ecg monitoring for next week
I now feel so embarrassed as from Friday I have had absolutely NO ectopic beats and all back to normal
Im so fed up of feeling anxious about my health
I think I should go ahead with the tests in case they start up again
But what if they find something else for me to worry about re my heart?
Feeling so up and down as this is my second bc the first being triple negative 10 years ago and this one being highly oestrogen driven
Anyone else had ectopic heart beats? How long did they last? Did they stop completely?


I’m so sorry that you are experiencing this . I have had an irregular heartbeat for nearly 20 years now . As soon as I felt it I asked to be investigated as I was awaiting a small gynae op and a friend had hers cancelled for the same reason. The way you describe it - somehow knowing that you’ve missed a beat then a real thud sounds very familiar. I had a 24 hour tape done which showed various irregularities but none serious or requiring medication. Irregularities are quite common as you get older and don’t always need treatment. I do still experience still experience episodes ( especially if I’m ill ) when I know it’s happening though there were no problems before / during / after my lumpectomy .

When I started Anastrozole for the first few weeks I experienced 2 hot flushes every hour for the first 3 weeks or so and every hot flush was accompanied by a loud thumping heart beat though it didn’t sound or feel irregular. It was scary though. After about 3 weeks my heart settled and after a couple more weeks the flushes themselves eased quite a bit as well - so perhaps it will settle down as your body adapts to the Letrozole .
Ultimately based on my Pathology results / Predict score and with the support of my Breast Care Team I decided I wouldn’t take an AI anymore though that was more to with my joints than my heart .

A couple of things I would recommend - forgive me if you know about them . Firstly control your caffeine intake , secondly when you feel it happening try to relax as it tends to get worse with stress . I take a Magnesium supplement which I find helpful ( but discuss with your Dr. ) I’m really glad that you have a helpful GP and that you’re getting investigated and so quickly . When you have your 24 hour tape make sure you do your normal activity and fill in the diary as they will want to know how your body responds when you are exercising etc also what time you took your Letrozole and any other meds you are on.

Wishing you all the best with it. Xx


Hi Joanne and thank you so much for your reply
Yes im doing decaf tea only and think because the gp was reassuring i have relaxed somewhat
I too have a low Predict score, only 1 percent benefit so feel quite conflicted
I have no other side effects but do worry about my bones as have osteoporosis
Im starting on bisphosphonates soon
Im 69 btw
Anyway thanks so much for responding, Saturday nights can be more worrisome as I know GP and BC clinic are closed
Best wishes Sue

Hi @Sue123

Sorry to hear you are having irregular heart beats. I’m 55 and have been on medication for supra ventricular tachycardia (fast heart beat above the ventricles with no specific reason - atrial fibrillation comes in the same bracket and can be quite common as we age). I was a regular gym user and have used fitness devices which recorded irregular fast heart rates, sometimes at rest for no apparent reason. I kept a diary to help with diagnosis which took several years as ECGs, stress/exercise test and 24 hour monitor didn’t show anything. During end of 2020 it happened for over 20 minutes and I was taken to GP surgery who caught the irregular rhythm on a ECG. Saw cardiologist, had the extra tests and been on medication ever since, which after a few tweaks, generally control the tachycardia.

Sometimes mine feel like a very strong heart beat like a thud and missed beat, they didn’t seem worried about this. When it’s a very fast rhythm it beats that fast you can barely take a pulse, I feel it’s fast and try to breathe through it, some people can get dizzy or pass out ( never happened to me).

I’m on Letrozole and the leaflet states less common side effects as fast heart rate (palpitations). I’ve just seen my cardiologist and she wasn’t bothered about the list of medications I gave her to look at.

I have found this on BCN which might be worth a read
Side effects of letrozole (Femara) | Breast Cancer Now.

Well done talking to your BC nurse and seeing the GP and that they are now organising tests to check. It must be very difficult being diagnosed two times with breast cancer and now this. I totally get it, I thought my heart issue was already a problem and I’m asthmatic, now I’ve got breast cancer. It’s totally understandable to think why me, why something else, haven’t I had enough. If it would help it might be worth a phone call to a breast cancer now nurse to talk this through as well. 0808 800 6000 Mon to Fri 9-4 Sat 9-1.

MacMillan have a helpline open 7 days a week 8-8 if you feel the need to talk to somebody tomorrow.

I hope your tests give you the answers you need.:smiling_face_with_three_hearts:

Thanks for your kind and informative reply naughty boob ( love the name)
Yes i told my GP about possibly extra beats can be due to letrozole but she rightly has organised these tests to check
I remember having these ‘ missed beats’ during my menopause so it seems logical that further reduction in oestrogen may bring those symptoms on again
I haven’t had any missed beats for 2 days now so am pleased and hopeful they will continue to stay away or at least reduce
Wishing you good health, Sue x

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Hi …i have this with letrozole…sometimes feel like my heart is racing …around 115 per minutes… othertimes skipped beats…had x 2 24 hour traces…they said its within a safe range so can live with it safely …been.like this 3 years now…sometimes no issues at all…no rhyme or reSon to it at all

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Thanks for your message Cat
I feel calmer knowing that others have had similar symptoms after taking letrozole
Best wishes Sue

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I’ve had these irregular beats as well, like you describe them. They seem to happen when I am stressed.

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@Sue123 hi, your post caught my attention. I had my mastectomy in September 2022 and started Letrozole in October 2022. I am experiencing ectopic heart beats for a while now not realizing that the culprit may be Letrozole. I too had a holter monitor test done just last week. The ECG I had done last year was normal. However I can feel the irregular heart beat very frequently. Waiting on my cardiologist’s interpretation of my holter test result. Let me know how it goes for you. Wishing you the best.


Sorry to read this, and you understandably feel anxious about it.

I had the same when I was on Tamoxifen for 2 years and had a 24 hour ECG and bloods. They all came back okay but I still had the irregular heartbeat! Sometimes if you’re a bit anaemic it can cause this. Drs don’t usually worry about low iron unless it’s on the floor but sometimes if you’re the lower end of normal it can still impact. Caffeinated drinks too can make things worse.

If you’re feeling anxious this can inevitably happen so try some relaxation techniques too. I found that if my heart was skipping I just did deep breathing and it stopped.

I’m sorry that you have had a second bout of breast cancer. The worry of this won’t have helped so I’m wishing you well, and hope things calm down.

Take care x


Hi Sue 123, Yes I have had ectopic beats for many years and they can be so worrying, especially when they come close together, but they can come and go. My advice - go for the tests, they will know if letrozole can be a factor. Explain that they seem to have settled down, if there is a problem they will be able to see it. Mine was first spotted by a midwife when I was carrying my son, he is a Dad himself now! Good luck, setting your mind at rest may reduce them.


Yes Siggi I’ll let you know the outcome of the tests
Let me know how you get on x

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