The indications for defibrillators are ventricular fibrillation, chronic atrial fibrillation, paroxysmal supraventricular tachycardia and sustained atrial flutter and other cardiac diseases. And contraindications include slow arrhythmias, severe hypokalemia, etc. 1. Indications: Defibrillators are commonly used in rescue work where patients suddenly develop severe arrhythmias. The patient’s ECG may present as ventricular fibrillation, chronic atrial fibrillation, paroxysmal supraventricular tachycardia and sustained atrial flutter. A defibrillator is also required for atrial flutter with 1:1 conduction. These types of arrhythmias, especially when drug therapy is ineffective, can be terminated by an electric defibrillator with a certain amount of current energy to normalize the rhythm. 2. Contraindications: The contraindications to defibrillators include slow arrhythmias, severe hypokalemia, etc. And digitalis overdose induced arrhythmia, left atrial huge and atrial fibrillation lasting more than one year, also avoid using defibrillator. Moreover, they are also contraindicated in patients with chronic unstable ventricular rate and in patients with atrial fibrillation, atrial flutter and atrial tachycardia with high or complete conduction block. There are more types of defibrillators and more types of arrhythmias, and their use needs to be judged by a doctor.