The short answer
Cardiac monitoring exists because treatment-related weakening of the heart is silent early, measurable before symptoms, and usually manageable when caught in time.
LVEF is the percentage of blood the main pumping chamber ejects per beat; normal is roughly 50 to 70%.
Echocardiogram and MUGA measure the same thing by different means, and neither is painful.
Anthracycline heart risk rises with the total amount received over a lifetime — low single digits at the doses most people reach, climbing steeply at the highest cumulative totals. Your team tracks your lifetime number; it is worth asking for.
Trastuzumab comes with heart-function checks on a fixed schedule: before starting, regularly throughout treatment, and for at least two years after adjuvant therapy ends.
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The full explanation.
When to get help sooner
- Call 911 or go to an emergency department if chest discomfort does not pass within a few minutes, if you cannot catch your breath at rest or wake up gasping, or if you faint or nearly faint. Do not wait to see whether it settles.
- Call your care team the same day if your heart is racing or beating irregularly, if breathlessness has appeared with mild activity or when lying flat, or if the scale has jumped over just a few days.
- Call your care team within a day or two if your ankles, legs, or abdomen have begun to swell, or if unusual fatigue and dizziness have crept in.
These symptoms have many harmless causes during cancer treatment. But they are worth checking, rather than waiting until your next scheduled echocardiogram (heart ultrasound).
Why the heart gets watched
A small number of effective cancer treatments can weaken the heart muscle's pumping ability. Monitoring exists for a few reasons. That weakening is usually silent at first. It develops gradually. It is measurable well before you would feel anything. And it is often reversible or manageable when caught early.
Being scheduled for echocardiograms is not a sign that your heart is failing. It is the mechanism by which that outcome is avoided.
What is being measured
Left ventricular ejection fraction, or LVEF, is the percentage of blood the heart's main pumping chamber pushes out with each beat. A normal heart does not empty completely. Typical values sit around 50% to 70%.
The number comes from one of a few tests. An echocardiogram uses an ultrasound of the heart, involving gel and a probe. A MUGA scan is a nuclear medicine study that measures the same thing using a small radiotracer. Cardiac MRI is used when the pictures need to be more precise. None of these tests hurt.
Your team is watching the trend more than any single value. A drop from your own baseline matters more than where you happen to fall within the published normal range.
Anthracyclines
Doxorubicin and related drugs carry a boxed warning for heart muscle damage. The risk grows with the total dose received over a lifetime.
The prescribing information estimates the chance of heart failure as a curve, not a cliff: low single digits at the cumulative totals most treatment plans reach, rising steeply toward the highest lifetime totals. The exact step-by-step figures are prescriber material — what matters on your side is that the curve exists and that your total is being tracked against it.
This is why oncologists track lifetime dose carefully. It is also why the label advises checking heart function before treatment, during it, and afterward — more frequently as the cumulative total grows. Prior radiation to the chest, and other heart-affecting drugs given alongside, raise the risk further.
Trastuzumab and HER2-targeted therapy
Trastuzumab can cause a decline in ejection fraction that is frequently reversible when the drug is held. Its label sets a fixed measuring schedule: immediately before starting, at regular points all the way through treatment, at completion, and continuing for at least two years after adjuvant therapy finishes. Your team calendars those scans; keeping them is your half of the arrangement.
The label defines exactly how large a fall from your own baseline forces a hold, and how often to remeasure while holding — numeric rules your oncologist and cardiologist apply to your scans, not ones to apply yourself. Treatment often restarts once the number recovers.
In the registration trials, congestive heart failure occurred in about 2% of treated patients. The risk was highest when the drug was combined with anthracyclines.
Who is considered higher risk
ASCO's guidance identifies groups warranting closer attention.
- Higher-dose anthracycline exposure.
- Chest radiation of 30 Gy or more, with the heart in the field.
- Anthracycline followed by trastuzumab.
- Age 60 or older at treatment.
- Two or more cardiovascular risk factors, such as smoking, high blood pressure, diabetes, high cholesterol, or obesity.
- Pre-existing heart problems, including a borderline ejection fraction.
A baseline assessment, including history, exam, and an echocardiogram, is advised before starting. An echocardiogram between six and twelve months after finishing is reasonable for higher-risk patients.
What happens if the number drops
A fall in LVEF typically leads to a few things. Doctors hold the drug rather than abandoning treatment. They refer you to cardiology or a cardio-oncology clinic. They may start heart medications, such as ACE inhibitors or beta blockers, which often help function recover.
Decisions about continuing cancer therapy are made jointly. Your team weighs your cancer risk against your cardiac risk. These decisions are individual, not automatic.
Sources
Words to know
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Common questions
Does needing an echocardiogram mean something is wrong with my heart?
No. A baseline study is taken before treatment starts precisely so later measurements have something to compare against. Monitoring exists to catch change early, at a stage where it is usually reversible or manageable.
What is the difference between an echo and a MUGA?
An echocardiogram is an ultrasound using gel and a probe on your chest. A MUGA is a nuclear medicine scan using a small radiotracer. Both estimate ejection fraction; the choice usually depends on image quality and what your center uses.
My LVEF dropped. Does treatment stop?
Often it is held rather than stopped. The label sets exact thresholds for how big a fall triggers a hold and how often to recheck — decisions your oncologist and cardiologist make from your own numbers. Many people resume once the ejection fraction recovers.
Why does my oncologist track my total lifetime anthracycline dose?
Because the risk of cardiomyopathy is proportional to cumulative exposure: modest at the totals most treatment plans reach, and climbing steeply at the highest lifetime totals. That is why checks become more frequent as your cumulative dose grows, and why the lifetime number follows you between hospitals.
What symptoms should prompt a call?
New or worsening breathlessness, especially lying flat, swelling in the ankles, legs or abdomen, rapid weight gain over a few days, a racing or irregular heartbeat, chest discomfort, or marked new fatigue and dizziness.
Questions to ask your doctor
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Written by: Cancer ExplainedSources last checked: 2026-07-30 what this meansLast updated: 2026-08-21Next planned review: 2027-02-03
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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