The first steps that a physician takes when diagnosing ventricular tachycardia (VT) is to obtain a patient’s medical history and to give the patient a physical examination. Next, the physician may order blood tests and an electrocardiogram (EKG). The EKG is a sensitive test that measures the heart's electrical activity and displays it on a computer screen or printout for a physician to analyze. 

If the EKG is normal, but the physician still suspects an abnormal heart rhythm, then the patient may need to wear a portable EKG Holter monitor for 24 hours. This device monitors the heart rate for 24 hours, allowing physicians to diagnose nonsustained arrhythmias that occur outside of the physician's office. If the Holter monitor still doesn't record any arrhythmias, the patient may be given a different kind of event recorder that is activated by the patient only when the arrhythmia occurs. This will allow the physician to study the characteristics of their particular arrhythmia. 

Depending on the results of these tests, a more invasive test called an electrophysiology (EP) study may be performed. An EP study is a procedure in which a thin tube (catheter) is inserted into a vein or artery (e.g., in the groin) and guided to the heart, where it can perform specific measurements of the heart’s electrical activity and pathways. During the EP study, a physician may or may not be able to reproduce the patient’s VT. If it can be produced, the patient is at particularly high risk of going into cardiac arrest at some point in the future.

EP studies are also an important part of therapy for VT treatment. They are typically performed before surgery or catheter ablation. These precise studies can exactly locate the source of an abnormal rhythm, thus allowing physicians to exactly target the defective area.