Suzie Brown spent nearly eight months assuming the pounding palpitations in her chest were caused by stress. It took a chance glance at her fitness watch during a jog, and a nurse's hunch, to reveal she had an overactive thyroid.
Brown, an insurance claims manager from Heysham, Lancashire, first noticed the symptoms at 40. "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," she said. The episodes of thumping heartbeats and mild chest pains struck at random. "I could be picking up my eight-year-old daughter from school, or lying in bed, there didn't seem to be any pattern," said Brown, now 42.
One weekend in December 2024, four months after her symptoms began, her heart started pounding constantly and "very loudly" in her ears, with chest pains that kept her awake at night. "I was convinced I must be having a heart attack," she said. By the Tuesday, her father drove her to hospital while her husband, Ashley, 38, who also works in insurance, took their daughter to school. An ECG and blood tests ruled out a heart attack, and Brown was discharged.
Her symptoms continued. Brown began feeling hot and sweaty and wondered if it might be the perimenopause, despite her young age. Her GP had her fill in an online symptom checker, but nothing was flagged. Over the following months she lost a stone and a half, struggled to sleep, felt irritable and wired, and noticed her hair thinning and her eyes feeling dry and gritty.
In April 2025, out for a jog, she glanced at her fitness watch and saw her heart rate was 180 beats per minute, well above the healthy exercising rate of 90 to 153 for a 40-year-old. Her GP told her to go straight to A&E. Checks came back normal again, but Brown pushed back. "I said I wasn't happy and knew something was wrong," she said. A nurse asked further questions and suggested she might have an overactive thyroid, arranging a blood test that confirmed it.
What is hyperthyroidism
With hyperthyroidism, the thyroid gland produces too much thyroxine, the hormone that controls metabolism. High levels can cause a rapid, irregular heartbeat, sudden weight loss despite an increased appetite, anxiety, difficulty sleeping, heat intolerance and excessive sweating. Other symptoms include itchiness, passing large amounts of urine, thirst, an enlarged thyroid gland, thyroid eye disease and, in men, erectile dysfunction.
An estimated 800,000 to a million people in the UK have an overactive thyroid, with women twice as likely as men to be affected, according to the article. The most common cause is Graves' disease, an autoimmune condition in which antibodies over-stimulate the thyroid to produce too much hormone. It is not clear what triggers Graves' disease, but smoking may raise the risk.
Kristien Boelaert, a professor of endocrinology at the University of Birmingham and an adviser to the British Thyroid Foundation, said excess thyroid hormone overstimulates the heart, which along with the nerves and gut has a particularly high concentration of thyroid hormone receptors. "It can also cause faster transit through the gut, weight loss, tremor and heat intolerance, as well as a whole host of other symptoms," she said.
Boelaert said symptoms such as palpitations, sweating and trouble sleeping overlap with stress and cardiac conditions and can mimic classic menopause symptoms, making diagnosis tricky, particularly for women. Left untreated, the strain on the heart can lead to atrial fibrillation and a higher stroke risk. In rare cases, an uncontrolled overactive thyroid can develop into a life-threatening thyroid storm, with symptoms including high blood pressure, fever, sweating, shaking, vomiting and agitation, a medical emergency that can be fatal in up to 30 percent of cases.
More than eight months passed before Brown's condition was even mentioned, and she then waited a further four months to see an endocrinologist. 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 a diagnosis. Boelaert said a middle-aged woman with repeated bouts of significant heart palpitations should first be given a thyroid function test, since some women are misdiagnosed with conditions such as panic disorder or undergo unnecessary cardiac investigations before their thyroid is checked.
Two unnecessary heart procedures
That was the case for Michelle Smythe, 42, a mother of two from Maidstone, Kent, who underwent two unnecessary cardiac procedures after doctors wrongly diagnosed a heart complaint when she in fact had an overactive thyroid. She uses a pseudonym because of ongoing medical treatment. Her symptoms began during a pregnancy 15 years ago, when her heart rate shot up to 209 beats per minute.
"I was short of breath and shaking, it was really terrifying," Smythe recalled. She was diagnosed with supraventricular tachycardia, episodes of abnormally rapid heartbeat caused by faulty electrical signalling in the heart, and told she would need a cardiac ablation, a five-hour procedure using heat to destroy the triggering tissue, performed under local anaesthetic. "I found it extremely painful as morphine doesn't work for me," she said.
When the operation proved ineffective, doctors repeated it three months later. "Again, it didn't work and my palpitation attacks continued," Smythe said. It was only when a third ablation was being planned that her consultant finally ran a thyroid function test, revealing an overactive thyroid caused by Graves' disease. "I went through 17 months of hell having completely unnecessary heart procedures," she said. "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, Smythe's thyroid gland was so badly damaged it had to be surgically removed, and she will take an artificial form of thyroid hormone for the rest of her life. She was later awarded 6,000 pounds in compensation by the hospital. "All of this trauma could have been avoided had the right test been done at the right time," she said.
Recovery under way
Brown echoed the frustration. After her diagnosis, she was started on the drug carbimazole to control her thyroid levels, though it took another four months for her palpitations to subside while doctors found the right dose. Her palpitations are now 70 percent improved. "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," she said.
Derek Connolly, a consultant cardiologist at the Midland Metropolitan University Hospital, said palpitations are often caused by atrial fibrillation, high blood pressure and coronary artery disease. "One of the things you should absolutely screen everyone who comes in with palpitations for is thyroid disease, with a blood test," he said. "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."
