Myasthenia gravis and atrial fibrillation are two different diseases, and it is not possible to judge which is more serious; both have their own hazards. Myasthenia gravis refers to the neuromuscular junction transmission disorders, resulting in muscle contraction weakness, often first ptosis, double vision and other symptoms, with the progress of the disease, there may be hoarseness, arm and leg weakness, swallowing difficulties, chewing difficulties, etc., and may even be life-threatening. Atrial septal defect refers to atrial septal defect, a congenital heart disease, the disease has a certain family genetic predisposition, atrial defects of different ranges of size, the impact on heart function is also different, the larger the range of atrial defects, the greater the impact on heart function, the more serious the condition. Whether it is myasthenia gravis or atrial defects, you must go to the hospital in time, cooperate with the doctor to do a detailed examination, clear diagnosis and then targeted treatment.