Ever had the sensation of butterflies in your chest, rather than your stomach? Of course, it might have been a simple case of nerves or jitters (or even love!), but a fluttery heartbeat can also be a sign of a common condition called atrial fibrillation (AF).
The heart rhythm problem affects an estimated 1.5 million people in the UK, and experts estimate at least a third more - around half a million people - remain undiagnosed, leaving them at risk of suffering a life-threatening AF-related stroke.
With an ageing population, and with the chances of AF rising as you get older, this number is expected to double by 2050.
That's why this week's AF Association Global AF Aware Week (running until Sunday) is focusing on identifying undiagnosed cases through its 'Detect, Protect, Correct & Perfect' campaign.
The charity stresses that the first step towards finding out if you have AF is simply checking your own pulse to see if your heartbeat feels irregular.
Here's what you need to know about the condition.
What is atrial fibrillation?
AF is actually the most common arrhythmia (heart rhythm problem), affecting four out of every 100 people over the age of 65.
It occurs due to abnormalities within the heart's electrical signals. The upper chambers of the heart are responsible for receiving blood that's returning from your lungs, and controlling the normal (sinus) rhythm of the heart. However, when the electrical system in the atria (the heart's upper chambers) malfunctions, it causes an abnormally fast, irregular heartbeat - or atrial fibrillation.
What are the symptoms?
A person with AF may not feel any symptoms when their heart rate changes from normal sinus rhythm to atrial fibrillation, so the condition is often only detected by a doctor when they're performing a check-up for another health reason.
However, people with AF can sometimes feel a fluttering sensation or palpitations in their chest, where they're aware that their heart is beating very quickly and erratically, depending on how severe the condition is. They may also experience shortness of breath or chest pains, along with tiredness - in fact, sometimes it's these things that might trigger them to see their GP.
Of course, palpitations are very common and, often, don't mean that anything is wrong with your heart - but it's always a good idea to get symptoms checked out by a doctor if you're concerned.
Know your pulse
The AF Association points out that AF can be detected easily with a manual pulse check, and it urges people to check their own pulse regularly.
Trudie Lobban, founder and CEO of the AF Association, explains: "The use of a simple, manual pulse rhythm check can help identify many people with an irregular heart rhythm - it only takes 30 seconds and you can easily learn to take your own pulse.
"The more you're aware of your own pulse rhythm, the more likely you can identify when your heart has an irregular rhythm and seek advice from your doctor."
Who's at risk of developing AF?
The exact cause of AF isn't known. Although it can affect anyone of any age, it's more common as you get older. It's also more likely if you have certain medical conditions, including other heart problems such as heart valve disease, congenital heart disease, cardiomyopathy, pericarditis, heart failure, atherosclerosis and high blood pressure.
People with medical problems such as an overactive thyroid and diabetes are also at a higher risk, as well as those with lung diseases like pneumonia, asthma and COPD.
Lifestyle issues, such as obesity, smoking, drinking a lot of caffeine or alcohol, or taking illegal drugs (particularly amphetamines or cocaine), can also be risk factors for AF.
Despite this, there's often no obvious reason why AF develops - and it can sometimes even affect people who are physically very fit.
Is AF dangerous?
Left untreated or poorly monitored, AF can lead to serious complications such as heart failure and AF-related stroke.
These strokes occur when the arrhythmia causes the blood to pool in the heart, leaving a person at risk of forming a blood clot, which may then be carried to the brain where it can block the blood flow. According to the AF Association, someone suffers an AF-related stroke every 15 seconds, yet most can be prevented using anticoagulation therapy (blood thinners), such as Warfarin or other drugs.
Trudie Lobban says: "In the UK, we know there are over half a million people with undiagnosed AF, who are at risk of suffering a debilitating or life-threatening AF-related stroke."
She says that every year, nearly 16,000 people suffer an AF-related stroke, yet a fifth will only be diagnosed with the condition after the stroke. Worryingly, 20% of these people will die from their stroke.
"This cannot go on," insists Lobban. "During AF Aware Week, we are calling on all those involved in the management of AF to work together to help identify these undiagnosed patients and to reduce the numbers of AF-related strokes by a third over the next three years."