Cases of ventricular fibrillation (VF) are a medical emergency and are easily diagnosed by medical personnel with monitoring equipment. People who are at risk for VF but have not suffered an episode yet may be more difficult to diagnose. There There are a number of conditions that predispose people to VF and sudden cardiac death, especially a history of heart attack and coronary artery disease. A physician suspecting one of these conditions might conduct a number of tests to look for certain signs. These tests include: 

• During a medical examination, a physician can detect abnormal heart rhythms (arrhythmia) by listening to the heart with a stethoscope. Blood pressure may also be measured.
  
  
• Blood tests can check blood oxygen levels, electrolytes and hormone levels.
  
  
• Chest x-rays can reveal various abnormalities, including heart enlargement (hypertrophy) and lung dysfunction.
  
  
• An electrocardiogram (EKG) is often considered the best diagnostic tool when VF or any other type of arrhythmia is suspected. An EKG is a recording of the heart’s electrical activity as a graph on a moving strip of paper or video monitor. The highly sensitive electrocardiograph machine helps detect heart irregularities, disease and damage by measuring the heart’s rhythms and electrical activity at rest or while exercising (stress test). EKGs can be done by a physician in an office or hospital setting, or by a portable unit worn by the patient and measured over time (e.g., a Holter monitor or an event recorder).
  
  
• Echocardiogram. This test uses sound waves to visualize the structure and function of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation) or narrowing (stenosis). During this test, a Doppler ultrasound may be used to evaluate blood flow.
  
  
• Cardiac catheterization procedures may also be used to help a physician learn more about a patient’s specific arrhythmia. One such test, called an electrophysiology study (EPS), involves placing an electrode catheter into a blood vessel and feeding it all the way to the heart. Once in place, the heart sounds are recorded to find any irregular heart rhythms. This helps the physician to locate the exact origin and nature of an arrhythmia. The physician can also use the electrode to stimulate an arrhythmia to see how helpful medical treatments have been.

The tests used will depend on a number of factors, including the specific symptoms of a patient as well as his or her personal and family medical history.