Medical Oncologist
Blood counts
Palpitations during chemotherapy
Most often the heart is compensating for something else — fewer red cells carrying oxygen, not enough fluid, a fever, or anxiety. In those cases the heart itself is fine and is doing what it should. Less often, and more importantly, the heart is the problem, because some drugs affect heart muscle or rhythm. What matters is what comes with it.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
Why is your heart racing during chemotherapy?
Most often because the heart is compensating for something else — fewer red cells carrying oxygen, not enough fluid, a fever, or anxiety. In those cases the heart itself is fine and is doing exactly what it should. Treat the cause and the palpitations settle.
Less often, and more importantly, the heart itself is the problem. Some chemotherapy drugs affect heart muscle or rhythm, and treatment also raises the risk of clots. That is why palpitations during chemotherapy get checked rather than reassured away.
What matters is what comes with it
A fluttering that lasts seconds and settles, with no other symptoms, is usually benign. Palpitations with chest pain, breathlessness, fainting or a fever are a different situation and need the same day.
Tell your team if you have any existing heart condition or take heart or blood pressure medicines. It changes how this is assessed.
!
Go to the emergency department now
Chest pain, tightness or pressure · pain spreading to the arm, jaw or back · breathlessness at rest or coming on suddenly · fainting, or nearly fainting · a racing or irregular heartbeat that will not settle · palpitations with a fever · sweating and feeling suddenly very unwell · swelling of the ankles with breathlessness, or being unable to lie flat · pain and swelling in one leg. Go to the nearest emergency department and say clearly that the person is on chemotherapy and name the drugs.
Not sure whether this applies to you?
Ask an oncologistWhat it usually is
The causes, from common to serious
Listed so you understand why this gets investigated rather than dismissed.
A low haemoglobin
The commonest reason. Fewer red cells means the heart beats faster to move the remaining oxygen around. Comes with tiredness, breathlessness on stairs and looking pale, and it is confirmed on a blood test.
Usually settles
- Once the level is corrected
Not enough fluid
Vomiting, loose motions, poor drinking or a sore mouth. The heart speeds up to maintain blood pressure. Comes with dizziness on standing and dark scanty urine, and it corrects quickly with fluids.
This and a low haemoglobin together account for most palpitations during treatment.A fever or infection
The heart races with any fever. During chemotherapy that combination is an emergency in its own right, whatever is causing the palpitations. Take the temperature before anything else.
Medicines and stimulants
Steroids, some anti-sickness medicines, salbutamol inhalers, thyroid tablets, strong coffee and tea. Bring the full list — a timing change often resolves it.
Salts out of balance
Potassium, magnesium and calcium all affect heart rhythm, and all can shift with vomiting, loose motions or kidney changes. A simple blood test shows it.
The heart itself
Some chemotherapy drugs affect heart muscle or rhythm, and treatment raises the risk of clots in the lung. This is the less common group and the reason an echo test is often done before treatment starts.
What to expect
How it gets assessed
Usually straightforward. Pulse, blood pressure, oxygen level and temperature, then a heart tracing, then blood tests — the counts, the salts and the kidney and thyroid function. That combination explains the large majority of cases.
The heart tracing
A quick painless recording with stickers on the chest. It shows the rhythm at that moment. If the palpitations come and go, you may be asked to wear a monitor for longer so the episode gets captured.
An echo, if the heart is in question
An ultrasound of the heart, showing how well it is pumping. Many people have one before chemotherapy starts as a baseline, particularly with drugs known to affect the heart, and it may be repeated during or after treatment.
Why they ask which drugs you are on
Because a few specific chemotherapy drugs carry known heart effects, and knowing you are on one changes how carefully this is pursued. Carry your treatment card and be able to name your regimen, especially if you attend a hospital that does not usually treat you.
If you were given an echo before starting, ask what it showed and keep a copy of the report with your file.Day to day
What helps while the cause is dealt with
Keep drinking steadily through the day, judged by urine rather than thirst. Dehydration is the commonest fixable contributor and the easiest to put right at home.
Cut the obvious stimulants
Strong tea and coffee, energy drinks, and tobacco in any form. Alcohol too, which your team will usually ask you to avoid during treatment anyway. None of these caused the problem, and all of them make it more noticeable.
Sit down and breathe out slowly
When an episode starts, sit or lie down rather than carrying on. Breathing out slowly for longer than you breathe in settles the racing that anxiety adds on top. If it does not settle within a few minutes, or you feel faint, get help.
Keep a short record
When it happens, how long it lasts, what you were doing, and whether anything else came with it. Count the pulse at the wrist if you can. That note is worth more at the appointment than any description of how it felt.
Do not change heart medicines yourself
If you take tablets for blood pressure or the heart, keep taking them and take the boxes to the appointment. Doses sometimes need adjusting during treatment because weight and blood pressure change, but that is a decision for your doctor.
Anxiety genuinely causes palpitations, and it is common during treatment. It is a conclusion to reach after the physical causes are checked, not before.Leave a number, we will call you
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Being straight with you
What this page cannot tell you
It cannot tell you whether your heart is affected. The causes here run from not drinking enough to a clot in the lung, and they cannot be separated by how the palpitations feel. A heart tracing, blood tests and sometimes an echo are what answer it.
It also cannot tell you whether yours can wait. Brief fluttering that settles, with nothing else alongside, can usually be raised at your next contact. Anything with chest pain, breathlessness, fainting or a fever cannot, and if you are unsure, treat it as the urgent case.
What to do next
Take your temperature first — a fever changes everything. Keep drinking steadily. Cut strong tea, coffee and tobacco. Keep a short record of when episodes happen and what comes with them, and take your full medicine list and treatment card to the appointment.
Questions we are asked
Common questions about palpitations
Is a racing heart normal during chemotherapy?
It is common, and usually the heart compensating for a low haemoglobin, dehydration or a fever rather than a problem with the heart itself. Common is not the same as ignorable — it is worth reporting, because the causes are checkable and mostly treatable.
When is it an emergency?
With chest pain, breathlessness, fainting or nearly fainting, a fever, sweating and feeling suddenly very unwell, or a rhythm that will not settle. Also pain and swelling in one leg, which raises the possibility of a clot. Any of those means an emergency department the same day.
Could it be the steroids?
Quite possibly. Steroids commonly cause a racing heart, restlessness and sleeplessness in the days around each cycle. Never stop or reduce them yourself — they are tapered deliberately — but do mention the pattern, since the timing can often be adjusted.
Will a transfusion stop it?
If a low haemoglobin is the cause, usually yes, within a day. If palpitations continue after the level is corrected, that is worth reporting, because it points at something else — commonly fluids, salts or the medicines you are taking.
I have a heart condition. Does that change anything?
Yes, and make sure your oncology team knows before treatment starts. Some drugs are used more cautiously or avoided, an echo is usually done as a baseline, and symptoms are taken more seriously. Keep your cardiologist in the loop too.
Can anxiety cause this?
Yes, and it is common during treatment. But it is a conclusion to reach once the physical causes have been checked rather than an explanation offered first. Ask for the blood tests and the tracing, and then treat the anxiety, which is also worth treating.
Should I stop drinking coffee?
Cutting back on strong tea, coffee and any energy drinks is sensible while this is being sorted out, and stopping tobacco matters more. None of them caused the problem, but all make it more noticeable, and removing them makes the pattern easier to read.
What should I record before my appointment?
When episodes happen, how long they last, what you were doing, whether the beat felt fast or irregular, and what else came with it. Count the pulse at the wrist if you can. That is far more useful than describing the sensation.
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Sources
- Cancer Research UK — Cancer drugs side effects
- Macmillan Cancer Support — Heart problems and cancer treatment
- National Cancer Institute — Chemotherapy and You
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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