An ECG low voltage is generally defined as an overall ECG waveform of less than 0.5 millivolts. The level of the ECG waveform reflects the voltage level of the heart, so when the waveform is low it suggests low voltage. It is usually seen in obesity, pericardial effusion, pleural effusion and pneumothorax. 1. Obesity: Because the electrical activity from the heart has to pass through the lungs and the chest wall skin, obese people with thick chest wall skin fat will have poor R-wave increment and low voltage. It is recommended to exclude organic heart disease or respiratory disease, and then make it clear that it is physiological low voltage, which generally does not need special treatment. 2. Pericardial effusion: Pericardial effusion refers to the presence of excessive exudate or leakage fluid between the pericardium and the heart, which will affect the electrical conduction of the heart, and therefore low voltage of electrocardiogram will occur. 3. Pleural effusion: pleural effusion refers to the presence of excessive fluid between the lungs and pleura, which also affects cardiac electrical conduction pleural effusion, usually need to check the lung CT and thoracic ultrasound, usually a large amount of pleural effusion will cause R-wave reduction and low voltage. The causes of low voltage on ECG include emphysema, pneumothorax, dilated cardiomyopathy, etc. These diseases need to be clearly diagnosed and treated under the guidance of cardiologists, and it is recommended that low voltage on ECG be treated in a timely manner in order to avoid delaying the condition.