Medical Oncologist
Targeted therapy side effects
Slow Heart Rate and Dizziness — on Targeted Therapies
Some targeted therapies slow the heart rate as a direct drug effect. Most cases are mild and found on a routine pulse check, not felt as a symptom. The ones that need urgent attention are those where you feel it — dizziness, near-fainting, or chest discomfort.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed August 2026
- A known drug effect — Certain targeted therapies act on receptors in the heart as well as the tumour, slowing the pulse in some patients.
- Often discovered on monitoring — Many people with TKI-related bradycardia feel nothing and the slow rate is found at a routine clinic check.
- Symptoms change everything — Dizziness or light-headedness on a slow rate means the heart is not compensating. That needs same-day assessment.
- Fainting is an emergency — If you faint or nearly faint, go to the emergency department — not your next scheduled appointment.
17+
Cancer Specialists
on Panel
on Panel
96.9%
Breast Cancer
Survival Rate*
Survival Rate*
15,000+
Patients
Treated
Treated
4.8★
Google Rating
(800+ reviews)
(800+ reviews)
Some targeted therapies slow the heart rate by acting directly on cardiac tissue. Most cases are asymptomatic and found on routine monitoring. When you feel it — dizziness, light-headedness, or shortness of breath — your team needs to know the same day. Fainting, chest pain, or loss of consciousness means go to emergency now.
If a symptom below applies to you, do not wait for a callback. Call 1800-202-8726 or go to your nearest emergency department.
What is bradycardia from a targeted therapy, and is it dangerous?
Bradycardia means a heart rate slower than your usual. Certain targeted therapies — particularly some ALK inhibitors, VEGFR inhibitors, and HER2-directed agents — slow the heart rate as a known drug effect, not a sign that the treatment is failing or that you have a new heart disease.
Whether it is dangerous depends almost entirely on symptoms, not on the number itself. A rate that is slower than your usual but causes no dizziness, no breathlessness, and no fainting is usually managed with careful monitoring and sometimes a dose adjustment.
A slow rate that makes you feel dizzy — especially when you stand up — means the heart is not pumping enough blood to your brain in those moments. That needs same-day assessment, not watchful waiting at home.
You do not need to check your pulse at home unless your team asks you to. What you need to notice is how you feel. Any new dizziness, light-headedness on standing, or unusual fatigue alongside a sense of your heart beating more slowly is worth a call today.
Meet the Specialists
17+ senior cancer specialists. One panel for your case.
Trained at AIIMS, Tata Memorial, and leading international centres. Combined 150+ years of experience. Every complex case is reviewed by 3+ of them — together.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
Interventional Radiologist
Dr. Mohammed Imran
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
Surgical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
You do not have to work this out alone
A 45-minute consultation with a specialist who treats this every week.
How do you tell a mild slow heart rate from one that needs urgent attention?
| Feature | Asymptomatic — mention at next visit | Symptomatic — call today | Emergency — go now |
|---|---|---|---|
| How you feel | Normal; no dizziness or shortness of breath | Dizzy, light-headed, or unusually breathless | Near-fainting, fainted, or severe breathlessness at rest |
| On standing up | No change from your usual | Feel unsteady or light-headed for more than a few seconds | Nearly collapse or cannot stand safely |
| Chest symptoms | None | Mild awareness of your heartbeat or vague chest discomfort | Chest pain, pressure, or sense of heart pausing |
| Typically starts | Often found at a routine check weeks into treatment | Can develop gradually or after a dose change | Can be sudden or follow worsening of milder symptoms |
| What to do | Continue treatment; tell your team at your next appointment | Call your oncology team the same day | Go to the emergency department immediately |
Questions your family is likely also asking
Will the targeted therapy have to stop because of this?
Not necessarily. NCCN and ASCO guidance on TKI-related bradycardia describes a stepwise approach: asymptomatic cases are monitored closely, mildly symptomatic cases often need a dose hold or reduction, and severe or persistent cases may need the drug to stop. Many patients restart at a lower dose once the heart rate recovers. The decision weighs how much benefit the treatment is providing against the severity of the cardiac effect — your oncologist will walk through this with you specifically.
Are there medicines that make the slow heart rate worse?
Yes, and telling your oncology team about everything you take is one of the most important things you can do. Beta-blockers, certain calcium channel blockers, digoxin, and some antiarrhythmic medicines all lower heart rate independently of your targeted therapy. If you take any of these for blood pressure, a previous heart condition, or any other reason, your team needs to know so they can weigh the combined effect. The same applies to herbal medicines and supplements — some have cardiac effects not listed on the packet. Do not stop a heart medicine without advice, but do disclose everything.
Can I exercise or do physical activity while this is happening?
Strenuous exercise while your heart rate is significantly slower than usual, or while you have any dizziness, is not safe. Your heart may not be able to increase its output enough to meet the demand of vigorous activity. Light activity such as gentle walking is generally manageable if you have no symptoms and your team knows about the bradycardia. If you feel dizzy or breathless on any exertion, stop immediately, rest, and tell your team. Wait for their guidance before returning to a vigorous routine.
What monitoring will my team do?
Your team will check your pulse at clinic visits and may arrange an ECG to look at the heart's electrical pattern. If the bradycardia is symptomatic or persistent, they may refer you for a cardiology review. In some cases a 24-hour heart monitor records your rate across a full day, which shows whether the rate drops further at night or during activity. The frequency of monitoring depends on how slow your rate is and whether you have symptoms — the monitoring plan is adjusted as those change.
Will the heart rate go back to normal after treatment ends?
In most cases, yes. TKI-related bradycardia is generally a reversible drug effect — the rate tends to return toward your baseline once the drug is held or stopped. The speed of recovery depends on the specific drug and how long the bradycardia has been present. A small number of people have a pre-existing tendency to a slower rate that the drug uncovers rather than causes; your team will factor this in and may arrange cardiology follow-up if the rate does not recover as expected.
Did you know?
Bradycardia is one of the most consistently reported cardiac effects of certain ALK inhibitors, occurring in a meaningful proportion of patients and documented as an expected effect in prescribing guidance — not a rare or unpredictable event.
Because it is anticipated, your team watches for it from the start of treatment. Reporting any dizziness or light-headedness is the most important thing you can do to make that monitoring useful.
Source: NCCN Clinical Practice Guidelines; ASCO Cardiovascular Toxicity of Cancer Treatment guidance
Explore 108 more Side Effects, Emergencies & Daily Living topics
Side Effects - Symptom-Specific Deep Dives
- Abdominal Pain on Targeted Therapy: When to Worry
- Acne-Like Rash on EGFR Inhibitors: Why It Happens and How to Treat It
- Anaemia and Low Haemoglobin During Targeted Therapy
- Blood Clots and Stroke Risk on Targeted Therapy
- Blurred Vision and Eye Problems on Cancer Drugs
- Brain Fog and Memory Problems During Treatment
- Breathlessness and Cough on Targeted Therapy: Ruling Out ILD
- Constipation During Targeted Therapy
- Diarrhoea on Targeted Therapy: How to Control It at Home
- Dry Eyes and Light Sensitivity During Treatment
- Extreme Fatigue on Targeted Therapy: Causes and What Helps
- Extremely Dry, Cracking Skin on Cancer Tablets
- Fever During Targeted Therapy: Home Care vs Emergency
- Hair Thinning, Curling and Colour Change on Targeted Therapy
- Hand-Foot Skin Reaction: Prevention and Relief
- Headaches and Dizziness on Targeted Therapy
- Heart Function Drop (Low Ejection Fraction) on Targeted Therapy
- High Blood Pressure Caused by Cancer Drugs
- High Blood Sugar on PI3K and mTOR Inhibitors
- Infusion Reactions: What Happens and How They're Managed
- Interstitial Lung Disease (ILD): The Side Effect You Must Not Ignore
- Itching That Won't Stop on Targeted Therapy
- Kidney Function Changes on Targeted Therapy
- Loss of Appetite and Weight Loss During Targeted Therapy
- Low Magnesium and Electrolyte Problems on Anti-EGFR Antibodies
- Low Platelets on PARP Inhibitors and TKIs
- Low White Cells and Infection Risk on Targeted Therapy
- Mouth Ulcers and Mucositis: Practical Relief
- Muscle Cramps and Joint Pain on Cancer Drugs
- Nausea and Vomiting on Oral Cancer Drugs
- Osteonecrosis of the Jaw: Prevention During Bone-Targeted Treatment
- Paronychia and Nail Changes on Targeted Therapy
- Peripheral Neuropathy: Tingling and Numbness in Hands and Feet
- Protein in Urine (Proteinuria) During Treatment
- QT Prolongation: What It Means on Your ECG Report
- Raised Liver Enzymes (SGPT/SGOT) on Targeted Therapy
- Secondary Cancers After Long-Term PARP Inhibitor Use
- Severe Rash With Fever or Blistering: A Medical Emergency
- Skin Darkening, Depigmentation and Pigment Changes
- Slow Heart Rate and Dizziness on Certain TKIs
- Sun Sensitivity and Photosensitivity on Cancer Drugs
- Swallowing Difficulty and Reflux on Cancer Tablets
- Swelling of Face, Legs and Around the Eyes
- Taste Changes and Metallic Mouth on Cancer Drugs
- Tumour Lysis Syndrome: A Rare but Serious Early Complication
- Underactive Thyroid (Hypothyroidism) Caused by Cancer Drugs
- Unusual Bleeding or Bruising on Cancer Drugs
- Voice Changes and Hoarseness on Targeted Therapy
- Weight Gain During Long-Term Targeted Therapy
- When Diarrhoea Becomes an Emergency: The Rule You Must Know
- Wound Healing Problems on Antiangiogenic Drugs
Daily Living & Adherence
- Can I Drink Alcohol on Targeted Therapy?
- Can I Drive While on Targeted Therapy?
- Can I Fast for Religious Reasons During Targeted Therapy?
- Can I Have Dental Treatment While on Targeted Therapy?
- Exercise During Targeted Therapy: How Much Is Safe?
- Haircuts, Waxing, Facials and Tattoos During Treatment
- How Should Family Members Handle Your Cancer Tablets Safely?
- I Accidentally Took a Double Dose: How Serious Is It?
- I Missed a Dose of My Targeted Therapy: What Should I Do?
- I Vomited Right After Taking My Tablet: Do I Repeat the Dose?
- Managing a Household Routine Around Your Dosing Schedule
- Pets, Gardening and Infection Precautions
- Running Out of Medicine: What to Do About Refills and Shortages
- Safe Disposal of Unused Cancer Medicines
- Sex and Intimacy While on Targeted Therapy: Safety Questions
- Sleep Problems on Targeted Therapy and What Actually Helps
- Smoking and Targeted Therapy: How It Changes Your Drug Levels
- Travelling With Cancer Tablets: Flights, Security and Storage
Emergency & Red-Flag Triage
- Chest Pain or Palpitations During Cancer Treatment
- Emergency Contact Card: What to Keep in Your Wallet
- Fever Above 100.4F on Cancer Treatment: The 1-Hour Rule
- Heavy Bleeding, Blood in Vomit or Black Stools
- Not Passing Urine or Sudden Swelling All Over
- Severe Rash Spreading Rapidly With Mouth or Eye Involvement
- Sudden Breathlessness on Cancer Tablets: Go to Emergency or Wait?
- Sudden Confusion, Seizure or Weakness on One Side
- Sudden Severe Abdominal Pain: Ruling Out Perforation
- Sudden Vision Loss or Double Vision: What to Do Right Now
- Swollen, Painful Leg: Recognising a Blood Clot
- Uncontrolled Diarrhoea: The 6-Stool Rule Every Patient Should Know
- What to Tell an ER Doctor Who Doesn't Know Your Cancer Drug
- Yellow Eyes, Dark Urine or Severe Right-Sided Pain
Food, Drug & Supplement Interactions
- Antacids and Acidity Tablets Can Block Your Cancer Drug
- Anti-Nausea and Anti-Acidity Drugs That Prolong QT
- Anti-TB Treatment and Targeted Therapy: A Dangerous Combination
- Antibiotics and Antifungals That Interfere With Cancer Drugs
- Ayurvedic and Herbal Medicines With Targeted Therapy: The Real Risks
- Blood Thinners and Targeted Therapy: Managing the Bleeding Risk
- Contraceptive Pills and Hormone Medicines With Cancer Drugs
- Diabetes and Blood Pressure Medicines With Targeted Therapy
- Grapefruit, Pomegranate and Starfruit: Why They're Banned on Many Cancer Drugs
- Green Tea, Coffee and Caffeine on Targeted Therapy
- Homeopathy Alongside Targeted Therapy: What You Should Know
- How to Check Any New Medicine Against Your Cancer Drug
- Painkillers: Which Ones Are Safe on Targeted Therapy?
- Protein Powders and Immunity Boosters: Helpful or Harmful?
- Statins and Cholesterol Medicines During Cancer Treatment
- The Complete Do-Not-Take List for Common Targeted Therapy Drugs
- Turmeric, Ashwagandha, Giloy and Wheatgrass During Cancer Treatment
- Vaccines and Antivirals During Targeted Therapy
- Vitamin, Calcium and Iron Supplements During Treatment
Side Effects - General & Timeline
- Are Side Effects a Sign That the Drug Is Working?
- Side Effect Timeline: What Happens in Week 1, Month 1 and Month 6
- Targeted Therapy Side Effects: The Complete List by Drug Class
- Understanding Side Effect Grades 1 to 4 (In Plain Language)
- When to Call Your Oncologist Immediately: The Red Flag List
- Will a Dose Reduction Make My Treatment Less Effective?
Next step
Still not sure what applies to you?
Send your reports across and a senior medical oncologist will go through what they mean, what is known, and what the options actually are.
Common questions
Frequently asked questions
How slow does my heart rate have to be before it is dangerous?
There is no single number that separates dangerous from safe, and your own usual resting rate matters more than any textbook threshold. What your team weighs is how far the rate has dropped from your baseline, whether you have symptoms, and how those symptoms affect your daily functioning. A rate that would be unremarkable in a trained athlete could be a significant fall for someone whose resting rate is normally higher. Focus on how you feel rather than the number on a device, and call if you notice new dizziness, light-headedness, or unusual tiredness.
Which targeted therapies are most likely to cause a slow heart rate?
ALK inhibitors — including crizotinib, ceritinib, and alectinib — are among those most consistently associated with bradycardia. Some VEGFR inhibitors and HER2-directed agents have also been reported to slow the heart rate. The risk and severity vary between drugs even within the same class, and not everyone taking these medicines develops bradycardia. Your prescribing team will tell you whether your specific drug carries this risk and what monitoring is planned from the start.
I felt dizzy once and it passed quickly. Do I still need to call?
Yes. A single episode that resolves does not mean the problem is gone — it may mean the heart rate dipped and then recovered, or that you moved positions too quickly. Your team cannot assess what happened without knowing about it. Call and describe the episode: when it happened, how long it lasted, whether it came on standing up, and whether anything else was going on at the time. One brief episode reported promptly is much easier to manage than repeated episodes reported later.
Is it safe to take my targeted therapy today if I feel dizzy?
Not without speaking to your team first. If you feel dizzy and a dose is due, call your oncology team before taking it. They will advise whether to take it, hold it, or come in for assessment. Do not skip doses on your own judgment either, because your team may want to see you before you restart and the timing of treatment matters. If you cannot reach your team and the dizziness is severe or you feel faint, go to the emergency department rather than waiting.
Should I be checking my pulse at home every day?
Only if your team has specifically asked you to. Routine home monitoring is not necessary for everyone on a TKI, and checking frequently without guidance can create unnecessary anxiety about normal variation. If your team has asked you to track it, do so consistently — at the same time each day, at rest, before standing. A smartwatch or a simple pulse oximeter gives a reliable reading. What matters more than daily numbers is noticing a trend: a rate that is falling week on week, or new symptoms appearing alongside a rate you know is lower than your usual.