The diagnosis of tachycardia can be made from the symptoms presented by the person consulting or discovered by a doctor on examination or on the electrocardiogram.

It can also be an extreme emergency where the person loses consciousness.

After a clinical examination, the doctor performs or orders various examinations.

First a electrocardiogram (ECG), its trace reflecting the electrical activity of the heart. Thanks to sensors placed on different parts of the body (chest, wrist, ankles, etc.), the doctor can visualize the electrical signals of this organ and detect abnormalities.

A portable device, the Holter, allows continuous 24-hour heart rate monitoring. Thus, tachycardia occurring only under certain conditions may be detected. Other tests, such as an ultrasound of the heart (echocardiogram) is used to visualize the blood flow and to detect certain clots. An exercise test (ECG performed during an exercise test such as cycling) may also be prescribed to better understand the type of tachycardia involved.