For nearly eight months, Suzie Brown simply assumed the pounding palpitations in her chest were stress-related.

‘My dad had been diagnosed with terminal cancer so I was under immense stress – and as I was only 40, I didn’t think it could be anything serious,’ recalls Suzie, an insurance claims manager.

Nonetheless, the repeated random episodes of thumping heartbeats and mild chest pains left her terrified.

‘I could be picking up my eight-year-old daughter from school, or lying in bed – there didn’t seem to be any pattern,’ says Suzie, now 42.

But then one weekend in December 2024, four months after her symptoms first began, Suzie’s heart started pounding constantly and ‘very loudly’ in her ears – excruciating chest pains kept her awake at night.

‘I was convinced I must be having a heart attack,’ she says.

By the Tuesday, the family was so concerned that Suzie’s dad drove her to hospital, while her husband Ashley, 38, who also works in insurance, took their daughter to school.

Tests – an ECG (to measure heart rate) and blood tests – ruled out a heart attack, so Suzie was discharged.

But her symptoms continued.

Suzie, who lives in Heysham, Lancashire, also began feeling hot and sweaty, so wondered if it might be related to the perimenopause, despite her young age.

Her GP got her to fill in an online symptom-checker, but nothing was flagged up.

Over the following months, with the palpitations continuing, Suzie lost a stone and a half and had trouble sleeping.

Suzie suffered from chest palpitations for eight months before getting a diagnosis

‘Irritable and wired’, she also noticed her hair thinning and her eyes feeling ‘dry and gritty’.

Finally, out for a jog one day in April 2025, she happened to glance at her fitness watch and saw her heartbeat was 180 beats per minute (a healthy exercising rate for a 40-year-old is 90 to 153). She contacted her GP, who told her to go straight to A&E.

Once again, all the checks were normal – but this time Suzie stood her ground. ‘I said I wasn’t happy and knew something was wrong,’ she says. It was a nurse who – after asking a few more questions – suggested Suzie might have an overactive thyroid gland (hyperthyroidism) and arranged a blood test.

With hyperthyroidism, the gland produces too much of the hormone thyroxine, which controls metabolism.

High levels can cause bodily functions to speed up, leading to a rapid irregular heartbeat, a racing pulse, sudden weight loss despite an increased appetite, as well as anxiety and difficulty sleeping, heat intolerance and excessive sweating.

Other symptoms include itchiness, passing large amounts of urine (a higher metabolic rate causes the kidneys to filter blood faster), thirst, an enlarged thyroid gland (a goitre) or thyroid eye disease (when the immune system attacks the tissue behind the eyes, producing a characteristic ‘bulging’ appearance). It can also cause erectile dysfunction in men.

It’s estimated that around 800,000 to a million people in the UK have an overactive thyroid – with women twice as likely as men to be affected. The most common cause is Graves’ disease, an auto-immune condition caused by antibodies over-stimulating the thyroid gland to produce too much thyroid hormone. (It’s not clear what triggers Graves’, but smoking may increase the risk.)

Excess thyroid hormone overstimulates the heart – which, along with the nerves and gut, has a particularly high concentration of thyroid hormone receptors, explains Kristien Boelaert, a professor of endocrinology at the University of Birmingham, and adviser to the British Thyroid Foundation charity. This leads to a faster metabolism, and potentially heart palpitations.

‘It can also cause faster transit through the gut, weight loss, tremor and heat intolerance [feeling hot and sweaty], as well as a whole host of other symptoms,’ she told the Mail.

Symptoms of hyperthyroidism – such as palpitations, sweating and trouble sleeping – can overlap with other common conditions including stress and cardiac condition

But symptoms – such as palpitations, sweating and trouble sleeping – can overlap with other common conditions including stress and cardiac conditions – which can make diagnosis tricky, particularly for women, as they also mimic classic menopause symptoms, says Professor Boelaert.

This can often lead to delays in diagnosis – yet early identification of an overactive thyroid is crucial. Left untreated, the constant strain on the heart can lead to atrial fibrillation (an erratic heartbeat) and an increased risk of stroke. In rare cases, uncontrolled overactive thyroid can develop into a life-threatening ‘thyroid storm’ – where a sudden, massive release of thyroid hormones into the bloodstream tips the metabolism into overdrive.

Symptoms include high blood pressure, fever, sweating, shaking, vomiting and agitation: it’s a medical emergency that can lead to death in up to 30 per cent of cases.

Yet despite having classic symptoms of an overactive thyroid, more than eight months passed before the condition was even mentioned to Suzie. She had another four-month wait to see an endocrinologist, a hormone specialist.

Her experience is troublingly common. A 2023 survey by the University of Aberdeen of 1,200 people with thyroid disease found people waited on average four and a half years for their diagnosis.

Sometimes women with heart palpitations may be misdiagnosed with other conditions, including panic disorder. Others may have unnecessary cardiac investigations without first being tested for thyroid function – Professor Boelaert says that a middle-aged woman with repeated bouts of significant heart palpitations should be first given a thyroid function test.

But this was not the case for 42-year-old Michelle Smythe, a mother of two, from Maidstone, Kent, who underwent two unnecessary cardiac procedures because doctors wrongly diagnosed a heart complaint when in fact she had an overactive thyroid.

It was only after both procedures failed that she was finally given a blood test to check her thyroid function and the truth was revealed – despite having a family history of thyroid problems. Her symptoms began during her pregnancy 15 years ago, when her heart rate shot up to 209 beats per minute.

After she was started on the drug carbimazole to control her thyroid levels, Suzie's palpitations are 70 per cent improved

‘I was short of breath and shaking, it was really terrifying,’ recalls Michelle, who works as a caretaker and has asked to use a pseudonym because of ongoing medical treatment.

She was diagnosed with supraventricular tachycardia – episodes of abnormally rapid heartbeats caused by faulty electrical signalling in the heart – and told she’d need a cardiac ablation, when heat is used to destroy the tissue triggering the faulty signalling. The five-hour procedure was performed under local anaesthetic.

‘I found it extremely painful as morphine doesn’t work for me,’ says Michelle.

When the operation proved ineffective, doctors repeated it three months later.

‘Again, it didn’t work and my palpitation attacks continued,’ says Michelle.

It was only when planning a third ablation that her consultant finally did a thyroid function test, and Michelle was diagnosed with an overactive thyroid caused by Graves' disease.

‘I went through 17 months of hell having completely unnecessary heart procedures,’ she told Good Health. ‘I don’t understand why they didn’t do a thyroid blood test when I first started with palpitations.’

By the time she was diagnosed, her thyroid gland was so badly damaged it had to be surgically removed.

Michelle will now take an artificial form of thyroid hormone for the rest of her life.

She was later awarded £6,000 in compensation by the hospital.

‘All of this trauma could have been avoided had the right test been done at the right time,’ she says.

Suzie echoes this frustration. After her diagnosis with an overactive thyroid, she was started on the drug carbimazole to control her thyroid levels – although it would take another four months for her palpitations to subside while doctors tried to find the right dose for her.

Now her palpitations are 70 per cent improved.

But she adds: ‘The delays mattered because my symptoms were getting worse all the time – putting my heart under stress and me at risk of serious long-term symptoms.’

Professor Derek Connolly, a consultant cardiologist at the Midland Metropolitan University Hospital, says that palpitations are often caused by atrial fibrillation, high blood pressure and coronary artery disease.

But he adds: ‘One of the things you should absolutely screen everyone who comes in with palpitations for is thyroid disease – with a blood test.

‘That is a standard test, even though it is a relatively rare cause. In younger women with palpitations, I would be looking for thyroid disease.’