It's slightly more common in men than women and is more likely to develop as people get older. When electrical impulses travel along pathways to the heart muscle they trigger the muscle to contract, or beat. Whilst this system is working properly the heart beats regularly and without problem. However, if something damages or interferes with the transmission of these electrical impulses then the heart may beat faster and irregularly, called fibrillation. As a consequence of this the heart does not work as effectively as it should.
Many people also feel faint or light-headed.
When blood is not passed through the heart as effectively as it should be, other symptoms may occur. People may feel short of breath, especially when lying down flat, their ankles may become swollen, and they feel unusually tired for a great deal of the time. Those people who have suffered any damage to their heart, from a heart attack for example, or damage to the heart valves, are more likely to be affected by atrial fibrillation. Having diabetes, or an overactive thyroid gland producing too much thyroid hormone may also cause it as may having un-treated high blood pressure. Excess alcohol is commonly responsible too.