Feeling a fluttering heart while sleeping may be a result of an arrhythmia. For cardiac fibrillation the most common arrhythmia is atrial fibrillation, and patients with atrial fibrillation have an absolutely irregular heart rhythm. Patients tend to feel the heart fluttering during nighttime sleep as the symptoms of the heart are more pronounced. It is recommended that a 24-hour ambulatory electrocardiogram be performed to clarify the type of arrhythmia. It is also recommended to perform differential diagnosis for organic cardiovascular diseases. It is recommended to give ECG, cardiac enzymes, cardiac ultrasound and coronary artery imaging to clarify the condition. In addition, abnormal thyroid function, such as hyperthyroidism, may also appear to be significantly worse at rest, and comprehensive systemic treatment is recommended.