Heart Racing? Why Your Internal Engine Is Stuck in Overdrive: Hyperthyroidism & Medical Next Steps

If your heart feels like it's racing for no clear reason, your hands are shaky, or you're losing weight without trying, your body may be running in "overdrive." One possible cause is hyperthyroidism — a condition where the thyroid gland produces too much thyroid hormone.

Think of your thyroid as your body's engine regulator. When it releases too much hormone, your metabolism speeds up. Everything moves faster — your heart, digestion, energy use, and even your thoughts.

Here's what you need to know about hyperthyroidism, what causes it, how it's treated, and what steps to take next.

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What Is Hyperthyroidism?

Hyperthyroidism is a medical condition in which the thyroid gland (a small butterfly-shaped gland in the neck) produces excessive amounts of thyroid hormones — mainly T3 (triiodothyronine) and T4 (thyroxine).

These hormones control:

• Heart rate
• Body temperature
• Metabolism (how you burn calories)
• Energy levels
• Mood
• Digestion

When there's too much thyroid hormone in your bloodstream, your body's systems speed up.

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Common Symptoms of Hyperthyroidism

Symptoms can range from mild to severe. Some people notice subtle changes at first, while others feel dramatically unwell.

Common signs include:

• Rapid or pounding heartbeat (palpitations)
• Unexplained weight loss (despite normal or increased appetite)
• Anxiety or irritability
• Tremors (shaky hands)
• Heat intolerance or excessive sweating
• Trouble sleeping
• Fatigue or muscle weakness
• Frequent bowel movements
• Thinning skin or hair changes
• Irregular menstrual cycles
• Enlarged thyroid (goiter)

In older adults, symptoms may be more subtle, such as fatigue, depression, or unexplained weight loss — sometimes called "apathetic hyperthyroidism."

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What Causes Hyperthyroidism?

Several conditions can lead to hyperthyroidism. The most common causes include:

1. Graves' Disease

This is the most common cause. It's an autoimmune disorder where the immune system mistakenly stimulates the thyroid to produce excess hormone.

Graves' disease may also cause:

• Eye changes (bulging, irritation, double vision)
• Swelling in the lower legs (rare)

2. Thyroid Nodules

Overactive nodules in the thyroid (toxic nodular goiter or toxic adenoma) can independently produce excess thyroid hormone.

3. Thyroiditis

Inflammation of the thyroid (often temporary) can cause stored hormone to leak into the bloodstream.

4. Excess Iodine or Thyroid Medication

Too much iodine or overuse of thyroid hormone replacement can also trigger hyperthyroidism.

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Why a Racing Heart Matters

One of the most concerning effects of hyperthyroidism is its impact on the heart.

Excess thyroid hormone can cause:

• Fast resting heart rate
• Atrial fibrillation (irregular heart rhythm)
• High blood pressure
• Increased risk of heart failure (if untreated)

This doesn't mean panic — but it does mean the condition should not be ignored.

If you experience:

• Chest pain
• Severe shortness of breath
• Fainting
• Confusion

Seek urgent medical care.

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How Hyperthyroidism Is Diagnosed

Diagnosis typically involves:

Blood Tests

Doctors check:

• TSH (thyroid-stimulating hormone) – usually low in hyperthyroidism
• Free T4 and T3 – typically elevated

Additional tests may include:

• Thyroid antibody testing (for Graves' disease)
• Radioactive iodine uptake scan
• Thyroid ultrasound

Diagnosis is usually straightforward with blood testing.

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Treatment Options for Hyperthyroidism

The good news: hyperthyroidism is treatable. The best treatment depends on the cause, age, overall health, and severity.

1. Anti-Thyroid Medications

Drugs such as methimazole reduce thyroid hormone production.

Pros:

• Non-invasive
• Often first-line treatment
• May lead to remission in Graves' disease

Cons:

• Requires monitoring
• Rare but serious side effects (e.g., low white blood cells)

2. Radioactive Iodine Therapy

A commonly used treatment that shrinks or destroys overactive thyroid tissue.

Pros:

• Effective and widely used
• Non-surgical

Cons:

• Often leads to hypothyroidism (underactive thyroid), requiring lifelong thyroid hormone replacement

3. Surgery (Thyroidectomy)

Removal of part or all of the thyroid.

Pros:

• Immediate control
• Good option for large goiters or suspected cancer

Cons:

• Surgical risks
• Usually results in lifelong thyroid hormone replacement

4. Beta-Blockers (Symptom Control)

Medications like propranolol can reduce:

• Heart rate
• Tremors
• Anxiety

These do not treat the underlying cause but help manage symptoms.

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What Happens If Hyperthyroidism Is Left Untreated?

Untreated hyperthyroidism can lead to serious complications:

• Persistent heart rhythm problems
• Bone thinning (osteoporosis)
• Muscle weakness
• Thyroid storm (a rare but life-threatening emergency)

A thyroid storm includes:

• High fever
• Rapid heart rate
• Confusion
• Severe agitation

This is rare but requires emergency care.

Early diagnosis and treatment dramatically reduce these risks.

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When Should You See a Doctor?

You should speak to a doctor if you notice:

• Ongoing unexplained weight loss
• Persistent racing heart
• Shaking hands
• New anxiety that feels physical
• Heat intolerance
• Eye changes

Even if symptoms seem mild, it's worth checking.

If you're experiencing any combination of these symptoms and want to better understand whether they could be related to an overactive thyroid, you can use Ubie's free AI-powered Hyperthyroidism symptom checker to evaluate your specific situation and get personalized insights in just a few minutes.

However, an online tool is not a diagnosis. Blood testing is required to confirm hyperthyroidism.

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Living With Hyperthyroidism

With proper treatment, most people live normal, healthy lives.

Helpful strategies include:

• Taking medications exactly as prescribed
• Attending regular blood test monitoring
• Reporting new symptoms promptly
• Avoiding excess iodine supplements unless directed
• Managing stress and sleep

Once thyroid levels are controlled, many symptoms improve significantly within weeks to months.

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A Calm but Clear Takeaway

If your heart feels like it's racing and your body seems stuck in high gear, hyperthyroidism may be worth considering. It's a common and treatable medical condition — but it can have serious consequences if ignored.

The key points:

• A fast heartbeat plus weight loss and anxiety may signal hyperthyroidism
• Blood tests confirm the diagnosis
• Effective treatments are available
• Early care prevents complications

If you are experiencing severe symptoms such as chest pain, fainting, extreme shortness of breath, or confusion, seek emergency medical attention immediately.

For anything that could be serious or life-threatening, you should speak to a doctor right away. Even milder symptoms deserve medical evaluation to protect your heart, bones, and overall health.

Your body isn't meant to run in overdrive. If something feels off, listen to it — and take the next step toward getting answers.