context: There's a greater link between atrial fibrillation ( AFib) and thyroid disease than you might think. Both conditions can have an impact on your heart. You probably don't give much thought to your thyroid, or even really know it's there, until something goes wrong with it. It's a small gland in the front of your neck with what seems like a simple job: to make hormones. Sounds basic, but those hormones are powerful. They tell your body how fast or slow it should work. When your thyroid is too active, it's called hyperthyroidism. You get more hormones than you need, which is like stepping on an internal gas pedal. Everything speeds up, including your heart. If you take thyroid replacement hormone -- because your thyroid is underactive or your doctor removed it -- a dose that's too high can cause the same issue. And that rapid heartbeat can lead to AFib, where the top chambers of your heart start to quiver and it can't pump as much blood as normal. AFib also raises your chances for a stroke -- and that's something you don't want to ignore. In general, if you have AFib, an overactive thyroid isn't the most likely cause. But if you have hyperthyroidism, you have a much higher chance of getting AFib. And the odds go up as you get older, especially once you're over 60. It's the most common heart problem in people with overactive thyroids. Each condition has its own set of symptoms to keep an eye on. If you have hyperthyroidism, you may notice that you: Feel nervous, anxious, or irritable Have a heartbeat that's faster than normal or feels off Sweat more than usual Have trouble sleeping Get shakiness in your hands and fingers Have swelling near the front, bottom of your neck Feel tired or weak in your muscles Lose weight for no reason Get changes in your periods if you're a woman If you're older, the symptoms may be less clear. They may seem more like depression, where you don't feel like eating much and you stop spending time around other people. If you have AFib, you may get symptoms like: Heartbeat that feels off, like it's racing, quivering, fluttering, thumping, or flip-flopping Pain in your chest You feel confused Feel dizzy or light-headed Get tired or weak Find it hard to exercise because you tire quickly Get short of breath Sweat more than usual Talk to your doctor if you have symptoms of AFib or hyperthyroidism. It could be something else entirely, but she can help you know for sure. If you have chest pain, though, go to the emergency room because it could also be a sign of a heart attack. Your doctor will start with a physical exam and questions about your symptoms and health history. From there, you'll likely need different kinds of tests. Thyroid tests. You'll start with blood tests to check your levels of: Thyroid stimulating hormone ( TSH), which is made by the pituitary gland and tells your thyroid how much hormone to make. Low TSH usually means you have an overactive thyroid. Thyroid hormones, called T3 and T4. If they're high, you likely have hyperthyroidism. From there, you may get other tests, like imaging or more bloodwork, to look for what's causing the problem. AFib tests. You may get: Electrocardiogram, also called an ECG or EKG, to look at the electrical signals in your heart. It's the main test for AFib and takes just a few seconds. In some cases, you'll get a portable EKG to measure activity over a longer stretch of time. Echocardiogram, a video image of your heart that lets your doctor look for blood clots Stress test, which looks at how your heart reacts to exercise Chest X-ray to look at your heart and lungs The overall goal is to get thyroid hormone levels back to normal. But since AFib raises your odds of having a stroke, the first step is to get your heart under control. AFib treatment. To control your heart rate, you may get medicines like: Beta-blockers, usually the first choice Calcium channel blockers, if you can't take beta-blockers Digoxin, a more likely option if you also have heart failure Depending on your overall health and how likely you are to have a stroke, you might also get drugs to lower your chances of a blood clot. Common options include aspirin and warfarin ( Coumadin, Jantoven). Thyroid treatment. There are usually two steps here. You start with anti-thyroid drugs that prevent your thyroid from making too much hormone. You usually see improvement within 2 weeks. These drugs help settle things down, but they're not usually a long-term solution. For one thing, they may not work as well over time. And with continued use, they can have serious side effects, including liver damage. That's why the second step is often a treatment called thyroid ablation. You usually take one pill of radioactive iodine, which destroys your thyroid. After that you'll need to take a daily thyroid replacement hormone. For some people, removing the thyroid also prevents AFib.