Heart Palpitations and Weakness: What Can Cause Both Symptoms?
Feeling weak while your heart is racing, pounding, fluttering or skipping beats deserves more attention than the heartbeat sensation alone.
Sometimes an abnormal heart rhythm can reduce how effectively the heart pumps and cause weakness. In many other cases, the palpitations and weakness are two symptoms of the same underlying problem, such as anemia, thyroid disease, an electrolyte disturbance, low blood glucose or anxiety.
What Can Cause Heart Palpitations and Weakness Together?
- Arrhythmias such as atrial fibrillation or supraventricular tachycardia can cause palpitations, weakness, dizziness and shortness of breath.
- Anemia can cause weakness, fatigue, breathlessness, dizziness and a fast or irregular-feeling heartbeat.
- Hyperthyroidism may produce racing heart, tremor, heat intolerance, weakness and weight loss.
- Low potassium can cause both muscle weakness and abnormal or skipped heartbeats.
- Low blood glucose may cause weakness, trembling, sweating and a rapid heartbeat.
- Dehydration or acute illness may produce weakness together with a faster heartbeat.
- Anxiety or panic can cause palpitations, trembling, dizziness and a feeling of weakness.
- Heart valve disease and other cardiovascular disorders may also produce both symptoms.
Do Heart Palpitations Actually Cause Weakness?
Sometimes — but not always.
A palpitation is the sensation of being aware of your heartbeat. Simply feeling a heartbeat does not by itself reduce blood flow to the muscles.
However, some sustained arrhythmias can make the heart pump less effectively. If blood pressure or cardiac output falls, a person may develop weakness, dizziness, shortness of breath or fainting.
In many other conditions, weakness is not caused by the palpitation at all.
Instead, both symptoms result from the same underlying condition.
This is why finding the cause is more useful than assuming that a noticeable heartbeat is depriving every muscle of oxygen.
Arrhythmias That Can Cause Palpitations and Weakness
Atrial Fibrillation
AFib can cause a fast and irregular heartbeat together with weakness, fatigue, dizziness or shortness of breath.
Supraventricular Tachycardia
SVT can cause sudden episodes of rapid heartbeat, weakness, fatigue, dizziness or near-fainting.
PACs & PVCs
PACs and PVCs often feel like skipped or extra beats.
Occasional premature beats do not automatically explain significant generalized weakness, so another cause may need consideration.
For a broader explanation of racing, pounding, fluttering and skipped beats, see our heart palpitation symptoms cornerstone guide.
Weakness With a Fast or Irregular Rhythm Deserves Attention
When an arrhythmia lasts long enough to affect heart function, symptoms can extend beyond a simple awareness of the heartbeat.
They may include:
- Weakness or fatigue
- Dizziness
- Lightheadedness
- Shortness of breath
- Near-fainting or fainting
- Chest discomfort
This pattern is more important than an isolated brief palpitation without other symptoms.
Can Anemia Cause Palpitations and Weakness?
Yes.
Anemia means the blood does not have enough healthy red blood cells or hemoglobin to carry oxygen effectively.
Symptoms can include:
- Weakness
- Fatigue
- Shortness of breath
- Dizziness or lightheadedness
- Fast or irregular heartbeat
- Pale skin
The heart may beat faster as the body attempts to maintain oxygen delivery.
Does Vitamin B12 Deficiency Cause Pernicious Anemia?
The relationship is actually the other way around.
Pernicious anemia is one cause of vitamin B12 deficiency.
In pernicious anemia, the body cannot adequately absorb vitamin B12 because of problems involving intrinsic factor.
Vitamin B12 deficiency can then cause megaloblastic anemia, which may produce fatigue, weakness, breathlessness and lightheadedness.
Long-standing B12 deficiency can also damage nerves and cause:
- Numbness or tingling
- Balance problems
- Neurological weakness
Vitamin B12 should therefore be tested and treated according to the actual diagnosis, not assumed from symptoms alone.
Can Low Potassium Cause Palpitations and Weakness?
Yes.
Potassium plays an important role in nerve, muscle and cardiac electrical function.
Low blood potassium, called hypokalemia, may cause:
- Muscle weakness
- Muscle cramps or spasms
- Fatigue
- Skipped beats or palpitations
- Abnormal heart rhythms when severe
Causes may include vomiting, diarrhea, certain diuretics, hormonal disorders and other medical problems.
Do Not Treat Palpitations by Simply Eating or Taking More Potassium
Potassium replacement should be based on an actual potassium measurement and the underlying cause.
Severe hypokalemia may require medically supervised potassium replacement and ECG monitoring.
Importantly, too much potassium can also cause dangerous heart-rhythm abnormalities.
This is particularly relevant for people with kidney disease or those taking medicines that raise potassium.
Do not self-treat unexplained palpitations with potassium supplements or salt substitutes.
Can Hyperthyroidism Cause Both Symptoms?
Yes. Excess thyroid hormone can make the heart beat faster or irregularly.
Hyperthyroidism may also cause:
- Muscle weakness
- Tremor
- Heat intolerance
- Excessive sweating
- Weight loss
- Anxiety or restlessness
Therefore, palpitations and weakness can both arise from the thyroid disorder.
Read our detailed guide to thyroid problems and heart palpitations .
Thyroid Storm Is Different From Ordinary Hyperthyroidism
Thyroid storm is a rare, life-threatening form of severe thyrotoxicosis.
It may include:
- A very rapid heartbeat
- High temperature
- Agitation or confusion
- Severe weakness
- Serious systemic illness
Suspected thyroid storm requires emergency medical treatment.
Can Low Blood Sugar Cause Palpitations and Weakness?
Yes.
Falling blood glucose activates stress hormones that can produce:
- Fast or pounding heartbeat
- Trembling or shakiness
- Sweating
- Hunger
- Weakness
- Dizziness
- Difficulty concentrating
Hypoglycemia is particularly relevant in people using insulin or certain diabetes medicines, but there are other causes as well.
What Is Late Dumping Syndrome?
Late dumping syndrome is a specific disorder associated with rapid gastric emptying.
It most often occurs after certain operations involving the stomach or esophagus, although it can occasionally occur in other settings.
Symptoms typically appear 1 to 3 hours after a meal.
Food moves rapidly into the small intestine, which can lead to excessive insulin release and subsequent low blood glucose.
Symptoms may include:
- Weakness
- Shakiness
- Sweating
- Lightheadedness
- Fast or irregular heartbeat
- Difficulty concentrating
This is a relatively specific diagnosis and should not be used to explain ordinary palpitations after eating in someone without the relevant clinical history.
Can Anxiety Cause Palpitations and a Feeling of Weakness?
Yes. Anxiety and panic can activate the body’s stress response.
Symptoms may include racing heart, trembling, sweating, dizziness, shortness of breath and a feeling of weakness or exhaustion.
Hyperventilation may contribute to lightheadedness and tingling during an episode.
However, weakness or palpitations should not automatically be attributed to anxiety without considering other causes. See anxiety and heart palpitations .
Can Aortic Regurgitation Cause Palpitations and Weakness?
Yes, particularly when aortic regurgitation becomes significant.
In aortic regurgitation, the aortic valve does not close completely, allowing some blood to leak backward into the left ventricle.
Symptoms can include:
- Fatigue or weakness
- Shortness of breath
- Palpitations
- Lightheadedness
- Chest discomfort
- Reduced exercise tolerance
Valve disease is therefore a real cardiovascular cause worth considering when the clinical history or physical examination suggests it.
Other Causes Doctors May Consider
Dehydration
Significant fluid loss can cause weakness, dizziness and a faster heartbeat.
Fever or Infection
Acute illness can raise heart rate while also causing fatigue and weakness.
Medicines
Some medicines can alter heart rate, blood pressure, glucose or electrolyte levels.
Low Blood Pressure
Hypotension may cause weakness, dizziness and awareness of a compensatory faster heartbeat.
Heart Failure
Heart failure can cause weakness, fatigue, breathlessness and rhythm abnormalities.
Other Arrhythmias
Sustained fast, slow or irregular rhythms can cause both heartbeat awareness and systemic symptoms.
See the broader causes of heart palpitations cornerstone guide for the full differential.
What Tests May Be Needed?
The combination of weakness and palpitations can have cardiovascular and non-cardiovascular causes, so testing should be targeted to the history and examination.
Medical History & Examination
Your clinician will want to know whether the heartbeat is fast, irregular or skipped, how long it lasts and when the weakness occurs.
ECG / EKG
An ECG can identify many rhythm abnormalities if they are present during the recording.
Holter or Event Monitor
If episodes come and go, ambulatory ECG monitoring may help capture the actual rhythm during symptoms.
Complete Blood Count
A blood count can identify anemia, which is an important cause of weakness and a faster heartbeat.
Electrolytes & Blood Glucose
Potassium, magnesium, glucose and other tests may be appropriate depending on the circumstances.
Thyroid Testing
TSH and, when indicated, free T4 and free T3 can help identify thyroid dysfunction.
Vitamin B12 Testing
B12 testing may be appropriate when anemia, neurological symptoms or risk factors for B12 deficiency are present.
Echocardiogram When Indicated
Echocardiography may be useful if the history, examination or ECG raises concern about valve disease, cardiomyopathy or another structural heart problem.
How Are Heart Palpitations and Weakness Treated?
Treatment depends on the underlying diagnosis.
Arrhythmia
Treatment depends on the specific rhythm, symptoms, heart condition and individual risk.
Anemia
Treatment depends on why anemia developed — for example iron deficiency, B12 deficiency, blood loss or another medical condition.
Thyroid Disease
Treatment depends on the specific thyroid disorder. See our thyroid and palpitations guide .
Electrolyte Abnormality
Electrolyte replacement should be based on laboratory results, severity, kidney function and the underlying cause.
Low Blood Glucose
Treatment depends on the cause and severity of hypoglycemia, including whether diabetes medication is involved.
Anxiety
When anxiety is confirmed as an important contributor, evidence-based psychological and medical treatment may help reduce symptoms.
What About “Natural Treatments” for Weakness?
Foods such as bananas, almonds, milk, eggs, fruit or other nutritious foods can certainly be part of a balanced diet.
But they should not be presented as treatments for unexplained palpitations and weakness.
Likewise, ginseng, licorice and other herbal products are not appropriate universal treatments.
Some herbal products can affect blood pressure, potassium levels or interact with medications.
When weakness accompanies palpitations, finding the cause is more important than choosing a food or supplement intended to increase “energy.”
Weakness Changes How I Think About a Palpitation
If a patient tells me, “I feel my heart fluttering,” but otherwise feels well, I approach that differently from a patient who says, “My heart races and suddenly I feel weak or almost faint.”
I want to know whether the weakness occurs only during the heartbeat episode or continues between episodes.
I also ask about dizziness, shortness of breath, chest discomfort, bleeding, heavy menstrual periods, diarrhea or vomiting, diabetes medicines, thyroid symptoms and recent medication changes.
Those details help determine whether we should focus first on the heart rhythm, anemia, glucose, electrolytes, thyroid function or another medical problem.
When Should You See a Doctor?
Arrange medical evaluation if palpitations and weakness:
- Are new or unexplained
- Keep returning
- Are becoming more frequent
- Occur during exercise
- Are associated with significant dizziness
- Are accompanied by unusual breathlessness
- Follow vomiting, diarrhea or significant fluid loss
- Occur after a medication change
- Occur in someone with known heart disease or an arrhythmia
If dizziness is prominent, see our guide to dizziness and heart palpitations .
If the palpitations are occurring throughout much of the day, also read constant heart palpitations .
When Palpitations and Weakness Need Urgent Care
Seek urgent or emergency medical care if palpitations and weakness occur with:
- Chest pain or significant chest pressure
- Fainting or loss of consciousness
- Severe dizziness or near-fainting
- Severe shortness of breath
- Sudden severe weakness or collapse
- A sustained very fast or severely irregular heartbeat with significant symptoms
- New confusion or major neurological symptoms
- Other severe or rapidly worsening symptoms
If chest pain occurs with palpitations, see our chest pain and heart palpitations guide, but do not delay emergency care to continue reading online.
Heart Palpitations and Weakness: FAQs
Why do I feel weak when my heart is racing?
A sustained fast rhythm can sometimes reduce how effectively the heart pumps, leading to weakness, dizziness or breathlessness.
But a condition such as anemia, hyperthyroidism or low blood glucose can also cause both the fast heartbeat and weakness.
Can AFib make you feel weak?
Yes. Atrial fibrillation can cause palpitations, weakness, fatigue, dizziness and shortness of breath.
Can anemia cause palpitations and weakness?
Yes. Anemia can reduce the blood’s oxygen-carrying capacity, causing fatigue, weakness, breathlessness, dizziness and a faster or irregular-feeling heartbeat.
Can low potassium cause weakness and palpitations?
Yes. Hypokalemia can cause muscle weakness, fatigue and skipped or abnormal heartbeats.
Severe potassium abnormalities can be dangerous and should be treated according to blood-test results.
Should I eat bananas or take potassium for my palpitations?
Not without knowing whether your potassium is actually low.
Too much potassium can also cause dangerous heart-rhythm abnormalities, particularly in people with kidney disease or certain medications.
Can vitamin B12 deficiency cause weakness?
Yes. Vitamin B12 deficiency can cause anemia and neurological problems, both of which may cause weakness.
Pernicious anemia is one cause of B12 deficiency; B12 deficiency does not itself cause pernicious anemia.
Can thyroid problems cause palpitations and weakness?
Yes. Hyperthyroidism can cause a fast or irregular heartbeat together with muscle weakness, tremor, heat intolerance and weight loss.
Can anxiety cause palpitations and weakness?
Anxiety and panic can cause racing heartbeat, trembling, dizziness and a feeling of weakness.
However, recurrent symptoms should not automatically be diagnosed as anxiety.
What is late dumping syndrome?
Late dumping syndrome is caused by rapid gastric emptying and commonly occurs after certain stomach or esophageal operations.
Symptoms usually occur one to three hours after eating and may include low blood glucose, weakness, sweating, shakiness and a fast or irregular heartbeat.
When are palpitations and weakness an emergency?
Seek urgent medical care when the symptoms occur with chest pain, fainting, severe breathlessness, severe dizziness, collapse or other severe or rapidly worsening symptoms.
Continue Reading
Evidence Used for This Article
- American Heart Association. Symptoms, Diagnosis and Monitoring of Arrhythmia.
- American Heart Association. What Are the Symptoms of Atrial Fibrillation?
- Mayo Clinic. Heart Arrhythmia: Symptoms and Causes. Updated 2026.
- Mayo Clinic. Anemia: Symptoms and Causes. Updated 2026.
- MedlinePlus. Low Blood Potassium.
- MedlinePlus. High Blood Potassium.
- MedlinePlus. Vitamin B12 Deficiency Anemia.
- MedlinePlus. Pernicious Anemia.
- National Institute of Diabetes and Digestive and Kidney Diseases. Dumping Syndrome: Symptoms and Causes.
- Mayo Clinic. Aortic Valve Regurgitation: Symptoms and Causes.