What is an electrocardiogram (ECG, EKG)?
The electrocardiogram (ECG or EKG) is a noninvasive test that is used to
reflect underlying heart conditions by measuring the electrical activity of the
heart. By positioning leads (electrical sensing devices) on the body in
standardized locations, information about many heart conditions can be learned
by looking for characteristic patterns on the EKG.
How is an ECG (EKG) performed?
EKG leads are attached to the body while the patient lies flat on a bed or
table. Leads are attached to each extremity (four total) and to six pre-defined
positions on the front of the chest. A small amount of gel is applied to the
skin, which allows the electrical impulses of the heart to be more easily
transmitted to the EKG leads. The leads are attached by small suction cups,
Velcro straps, or by small adhesive patches attached loosely to the skin. The
test takes about five minutes and is painless. In some instances, men may require
the shaving of a small amount of chest hair to obtain optimal contact between
the leads and the skin.
What is measured or can be detected on the ECG
- The underlying rate and rhythm mechanism of the heart.
- The orientation of the heart (how it is placed) in the chest cavity.
- Evidence of increased thickness (hypertrophy) of the heart muscle.
- Evidence of damage to the various parts of the heart muscle.
- Evidence of acutely impaired blood flow to the heart muscle.
- Patterns of abnormal electric activity that may predispose the patient to
abnormal cardiac rhythm disturbances.
Quick GuideHeart Disease: Causes of a Heart Attack
A recording of the electrical activity of the heart. Abbreviated ECG and EKG. An ECG is a simple, noninvasive procedure. Electrodes are placed on the skin of the chest and connected in a specific order to a machine that, when turned on, measures electrical activity all over the heart.
What conditions may be diagnosed with an ECG
- Abnormally fast or irregular heart rhythms.
- Abnormally slow heart rhythms.
- Abnormal conduction of cardiac impulses, which may suggest underlying
cardiac or metabolic disorders.
- Evidence of the occurrence of a prior heart attack (myocardial
- Evidence of an evolving, acute heart attack.
- Evidence of an acute impairment to blood flow to the heart during an
episode of a threatened heart attack (unstable angina).
- Adverse effects on the heart from various heart diseases or systemic
diseases (such as high blood pressure, thyroid conditions, etc.).
- Adverse effects on the heart from certain lung conditions (such as
pulmonary embolus [blood clots to lung]).
- Certain congenital heart abnormalities.
- Evidence of abnormal blood electrolytes (potassium, calcium, magnesium).
- Evidence of inflammation of the heart or its lining (myocarditis,
What are the limitations of the ECG (EKG)?
- The EKG is a static picture and may not reflect severe underlying heart
problems at a time when the patient is not having any symptoms. The most common
example of this is in a patient with a history of intermittent chest pain due to
severe underlying coronary artery disease. This patient may have an entirely
normal EKG at a time when he or she is not experiencing any symptoms. In such
instances, the EKG as recorded during an exercise stress test may reflect an
underlying abnormality while the EKG taken at rest may be normal.
- Many abnormal patterns on an EKG may be non-specific, meaning that they
may be observed with a variety of different conditions. They may even be a
normal variant and not reflect any abnormality at all. These conditions can
often be sorted out by a physician with a detailed examination, and occasionally
other cardiac tests (for example,
echocardiogram, exercise stress test).
- In some instances, the EKG may be entirely normal despite the presence of
an underlying cardiac condition that normally would be reflected in the EKG. The
reasons for this are largely unknown, but it is important to remember that a
normal EKG does not necessarily preclude the possibility of underlying heart
disease. Furthermore, a patient with heart symptoms can frequently require
additional evaluation and testing.
Medically Reviewed on 8/31/2016
Medically reviewed by Robert J. Bryg, MD; Board Certified Internal Medicine with subspecialty in Cardiovascular Disease
"Basic ECG test" UptoDate. Updated July 15, 2016