Medical Oncologist
Heart and organ effects
Heart warning signs during chemotherapy
Chest pain and sudden severe breathlessness during chemotherapy are emergencies. Other heart warning signs are easier to ignore: breathlessness when lying flat, waking gasping at night, new ankle swelling and palpitations. They can have other causes, but only a doctor can tell, so report them the same day.
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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Get emergency help immediately for any of these
Chest pain, pressure, heaviness or tightness, especially spreading to the arm, jaw, neck or back · sudden severe breathlessness · fainting or collapse · a very fast, very slow or irregular heartbeat with dizziness, sweating or chest discomfort · coughing up pink, frothy phlegm · sudden confusion with breathlessness. Go to the nearest emergency department and say clearly that the person is on or has had chemotherapy.
The short answer
Which heart symptoms matter during chemotherapy?
Chest pain, breathlessness, swelling of the legs or ankles, palpitations, dizziness and fainting are the heart symptoms to take seriously. Chest pain and sudden severe breathlessness are emergencies. Two warning signs that people often ignore are breathlessness when lying flat, needing extra pillows or waking at night gasping, and ankle swelling that is new or steadily getting worse. Both can mean the heart is not pumping as well as it should.
Many of these symptoms have other causes during treatment, such as a low haemoglobin, infection, a blood clot, fluid from steroids or simply tiredness. That is exactly why they need checking rather than guessing. Only a doctor can tell the difference, and some causes need urgent treatment. Reporting early lets your team protect your heart and keep your cancer treatment on track.
Do not wait for your next appointment
New or worsening heart symptoms should be reported the same day, not saved for the next treatment visit.
Some medicines carry more risk
Anthracyclines, HER2-targeted treatments, fluorouracil, capecitabine, some targeted tablets and immunotherapy are more often linked with heart effects.
Family should know the signs
Relatives often notice breathlessness or swelling before the patient mentions it.
Keep the chemotherapy helpline number and the nearest emergency department address where the whole family can find them.Not sure whether this applies to you?
Ask an oncologistKnow the signs
Heart symptoms and what they can mean
- Chest pain or tightness
- Can signal reduced blood supply to the heart, spasm of the heart arteries with some medicines, or inflammation. Always an emergency.
- Breathlessness on lying flat
- Needing to sit up to breathe, extra pillows, or waking gasping can mean fluid is building up in the lungs because the heart is struggling.
- Ankle and leg swelling
- Swelling in both legs that is new or worsening can be a heart sign. Swelling, pain or redness in one leg may be a blood clot.
- Palpitations
- A racing, pounding, fluttering or irregular heartbeat can mean a rhythm change and needs checking, urgently if you feel faint.
- Breathlessness on mild activity
- Getting breathless walking a short distance or climbing a few stairs, when you could before, needs reporting.
- Dizziness or fainting
- Can reflect rhythm problems, low blood pressure or dehydration. Fainting needs emergency care.
Step by step
What to do if you notice a heart symptom
Decide how urgent it is
Chest pain, severe breathlessness, fainting or a racing heart with dizziness need emergency care now. Other new symptoms need a same-day call.
Call for help or your helpline
For emergencies, go to the nearest emergency department. For other symptoms, call your chemotherapy helpline and describe what is happening.
Describe the details
Say when it started, what brings it on, whether it is getting worse, and which treatment you are having and when you last had it.
Take your papers
Bring your treatment summary, medicine list and previous heart scan reports if you go to hospital.
Do not drive yourself
If you have chest pain, breathlessness or dizziness, ask someone to take you or call an ambulance.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Being straight with you
What this page cannot tell you
It cannot tell you whether your symptom comes from the heart or from something else. Breathlessness, swelling and palpitations have many causes during treatment, and only an examination and tests can tell them apart.
It also cannot tell you whether to continue your treatment. If a heart problem is found, your oncologist and a heart specialist will decide together. Do not stop any medicine on your own.
Mild symptoms still count
Slight breathlessness or mild swelling that keeps getting worse over days matters as much as a sudden symptom. Report the trend.
Weigh yourself if advised
Sudden weight gain over a few days can mean fluid build-up. If your team asks you to weigh daily, note the readings.
Older patients may have fewer classic signs
In older adults, heart problems may show as tiredness, confusion or reduced appetite rather than chest pain. Report any sudden change.
Diabetes can mask chest pain
People with diabetes may feel less chest pain. Unexplained breathlessness, sweating or nausea deserve attention.
Anxiety can feel similar
Panic can cause a racing heart and chest tightness, but never assume it is anxiety without being checked.
Rhythm changes can come and go
Palpitations that settle before you reach hospital are still worth reporting. A heart tracing or longer monitoring may be arranged.
Heart symptoms can appear after treatment
Some heart effects appear months or years later. Tell future doctors which treatment you had.
Keep a simple symptom record
Write down when a symptom happened, what you were doing, how long it lasted and whether it went away with rest. If you can, note your pulse and blood pressure at the time. A short, clear record helps doctors decide quickly whether the heart is involved and what tests are needed.
Know which of your medicines carry heart risk
Ask your team whether any medicine in your plan is linked with heart effects. Knowing this helps you and your family take symptoms seriously on the right days, and helps emergency doctors who may not know your treatment.
Home blood pressure readings help
If you have a home blood pressure machine and your team asks you to use it, keep a log. Very high readings, or very low readings with dizziness or fainting, should be reported the same day, especially with targeted tablets.
Symptoms during a drip need immediate attention
If chest pain, tightness, palpitations or breathlessness start while a medicine is running, tell the nurse at once. The drip can be stopped and you can be checked immediately.
What to do next
Learn the warning signs with your family, keep the helpline number handy, and report chest pain, breathlessness, swelling, palpitations or fainting the same day, or go to the emergency department for severe symptoms. Bring your treatment summary and never stop medicines without advice.
Commonly believed
Four beliefs about heart symptoms during treatment
"Breathlessness is just tiredness from chemotherapy."
It can be, but it can also be a heart problem, a clot, infection or a low haemoglobin. It needs checking.
"Swollen ankles are normal on steroids."
Some swelling can happen, but new or worsening swelling, especially with breathlessness, must be reported.
"Chest pain during treatment is gas or acidity."
Never assume. Some medicines can cause heart artery spasm. Chest pain needs emergency assessment.
"I should wait until my next treatment day to mention it."
New heart symptoms should be reported the same day. Waiting can allow a problem to become serious.
Questions we are asked
Common questions about heart warning signs
What heart symptoms should I watch for during chemotherapy?
Chest pain, breathlessness, breathlessness when lying flat, swelling of the legs or ankles, palpitations, dizziness and fainting.
Is breathlessness during chemotherapy serious?
It can be. It may come from the heart, lungs, a clot, infection or low haemoglobin. Report it the same day, and seek emergency care if it is sudden or severe.
Why does breathlessness lying flat matter?
It can mean fluid is collecting in the lungs because the heart is not pumping well. Report it promptly.
Are swollen ankles a heart problem?
They can be, especially if both legs swell with breathlessness. One swollen, painful leg may be a clot. Both need checking.
What should I do if I have chest pain?
Treat it as an emergency. Go to the nearest emergency department, do not drive yourself, and tell staff you are on chemotherapy.
Are palpitations dangerous?
Not always, but they can signal a rhythm problem. Report them, and get urgent help if you feel faint, dizzy or have chest pain.
Which medicines raise heart risk?
Anthracyclines, HER2-targeted treatments, fluorouracil, capecitabine, some targeted tablets and immunotherapy are more often linked with heart effects.
Can heart symptoms start after chemotherapy ends?
Yes, occasionally. Report new breathlessness or swelling, and tell any doctor about your past treatment.
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Sources
- American Cancer Society — Heart Problems
- National Cancer Institute — Heart Problems and Cancer Treatment
- British Heart Foundation — Cancer treatment and your heart
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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