Electrocardiogram (EKG)


An electrocardiogram, abbreviated EKG (sometimes ECG), is a diagnostic cardiology test that measures the electrical activity of the heart using an electrocardiograph machine. The results are shown as line tracings on a graph, revealing the waves of electrical activity in peaks and dips. Electrocardiogram results can be viewed in real time on a monitor, and hard copy of the tracings are usually printed out on a strip of graph paper.


An EKG can detect heart rate and heartbeat abnormalities known as arrhythmias (e.g., atrial fibrillation, ventricular arrhythmias), a heart attack, inflammation of the heart wall (pericarditis), angina, and other disorders such as hypertrophic cardiomyopathy, an abnormal thickening of the heart muscle without an obvious cause. An EKG is commonly performed on individuals with heart-related symptoms such as chest pain or a family history of heart disease. Family physicians and cardiologists do not often recommend performing EKG tests on healthy individuals because abnormal results can occur even without the presence of a heart condition or abnormality. EKGs, however, usually are performed on professional athletes and sometimes, depending on school policies, on high school and college athletes and long-distance runners to ensure that these individuals are able to participate safely in endurance sports. Although the precise purpose of performing an EKG is always to measure the heart's electrical activity, the reasons for measuring electrical activity vary from evaluating heart function to monitoring or diagnosing existing heart problems. An EKG may be performed to:


A nurse examines the electrical activity of a patient's heart on an electrocardiogram (EKG) machine. EKGs can detect problems with the heart by monitoring how fast or slow it's beating or if the heartbeat is weak or irregular.

A nurse examines the electrical activity of a patient's heart on an electrocardiogram (EKG) machine. EKGs can detect problems with the heart by monitoring how fast or slow it's beating or if the heartbeat is weak or irregular.

Electrodes placed on the skin and attached to the electrocardiograph machine are able to detect tiny electrical changes on the skin that correspond to the depolarization pattern of the heart muscle during each heartbeat. EKG results are shown on a graph, with the peaks and dips depicting electrical activity in voltage as it changes with time. As such, EKG results indicate the electrical activity and heart muscle contractions occurring in all four chambers of the heart, the heart rate and heartbeat, and blood flow passing through the atria and ventricles. Defects in heart structure, an abnormal heartbeat, or abnormal blood flow will alter the line tracings, producing different peaks (or spikes) and dips in the pattern of electrical activity. A series of different waves represent electrical activity in the depolarization and repolarization of the left and right atrial and ventricular chambers, including a P wave, QRS complex of waves, and a T wave. Results are compared to a normal tracing so that the radiologist or physician can interpret the differences and diagnose any heart defects or abnormalities in heart-valve function or heartbeat and rhythm.


Before undergoing an EKG, the individual will be asked to remove clothing from the upper body and to put on a hospital gown that opens in the back. He or she will be asked to remove all jewelry from the neck, arms, and wrists. The person undergoing an EKG may also be asked about any current medications, because some medications, both prescription and over-the-counter medications, may affect EKG results.


An EKG is typically performed in an examination room, either in a hospital, clinic, or doctor's office. The individual will usually be lying down, face up. Up to 12 electrodes (sometimes only 10) will be placed on the skin in specific areas of the chest (chest leads) and on the limbs (limb leads). A special gel (electrode paste) will be applied to each area before placing the electrodes; the gel helps to conduct electrical impulses. The electrodes are connected by wires to the electrocardiograph machine. While the machine is running, the individual will be asked to lie still and breathe normally, although it may be necessary at some point to hold the breath briefly. Results of the test are visible on a monitor and are also printed out as a tracing of electrical activity on a special strip of graph paper. The whole test takes only 5–10 minutes and, depending on the reason for the test, results may be read immediately, transferred electronically to be read at a remote location, or the strips with results will be prepared for later reading by the individual's doctor or a cardiologist.

Automated external defibrillator—
A portable electronic device that is used to diagnose cardiac arrhyth-mias, including ventricular fibrillation and ventricular tachycardia, and can apply electrical therapy to defibrillate the heart, stop an irregular heartbeat, and restore normal heart rhythm.
Cardiopulmonary resuscitation—
A lifesaving emergency medical procedure that is performed to restore the heartbeat and normal heart rhythm in someone whose heart has stopped.
In cardiology, the loss of polarization in heart muscle cells, which represents a loss of differences in electrical charge (positive/negative) between the inside and outside of the cells and the subsequent passage of electrolytes through the cell membrane.
Hypertrophic cardiomyopathy—
A thickened heart muscle without an obvious cause, resulting in abnormal electrical activity of the heart.
Sudden cardia death (SCD)—
Also called sudden cardiac arrest, SCD refers to sudden, unexpected death caused by loss of heart function. It occurs most often in adults in mid-30s to mid-40s, and in men more than women.

An EKG also may be performed in conjunction with certain other diagnostic procedures, including cardiac stress testing, computed tomography angiograph, and magnetic resonance angio-graphy. Another form of EKG, used in clinical cardiac electrophysiology, requires the use of a catheter to measure electrical activity. This is performed by a cardiologist. Continuous EKG monitoring is used in the hospital for the constant monitoring of patients with critical illnesses.


When the electrodes are removed from the chest and limbs, the electrode paste will be cleaned from the electrode sites. No other aftercare measures are needed after undergoing an EKG.



No side effects are associated with having a non-invasive EKG performed. The test is painless and harmless. However, a stress EKG may involve exercise that can possibly result in certain heart-related symptoms in individuals with some types of abnormal heart function.


A normal pattern of electrical activity shown in the line tracings of an EKG indicates normal heart structure and function. Results of an abnormal EKG may indicate defects in the heart's shape or size or heart rate, heart rhythm abnormalities, a recent heart attack, the effects of certain medications, and the presence of electrolyte abnormalities. It must be remembered, however, that an abnormal result can be found even without an existing heart condition or disorder.



Benson, Roy T., and Declan Connolly. Heart Rate Training. Champaign, IL: Human Kinetics. 2011.

Sharkey, Brian J., and Steven E. Gaskill. Fitness and Health. 7th ed. Champaign, IL: Human Kinetics, 2013.


Harmon, Kimberly G., et al. “Incidence, Etiology, and Comparative Frequency of Sudden Cardiac Death in NCAA Athletes: A Decade in Review.” Circulation 132, no. 1 (July 7, 2015): 10–9.

Leischik, Roman, et al.“Pre-participation and Follow-up Screening of Athletes for Endurance Sport.” Journal of Clinical and Medical Research 7, no. 6 (June 2015): 385–92.

van der Wall, E. E. “ECG Screening in Athletes: Optional or Mandatory?” Netherlands Heart Journal 23 (July 2015): 353–5.


Healthwise Staff. “Electrocardiogram.” WebMD. http://www.webmd.com/heart-disease/electrocardiogram#1 (accessed February 26, 2017).

Jauhar, Sandeep. “EKG Screening for College Athletes.” New York Times. http://www.nytimes.com/2016/01/26/opinion/ekg-screening-for-college-athletes.html?_r=0 (accessed February 26, 2017).

National Heart, Lung, and Blood Institute (NIH). “What to Expect during Echocardiography?” U.S. Department of Health and Human Services. https://www.nhlbi.nih.gov/health/health-topics/topics/echo/during (accessed February 26, 2017).


American College of Sports Medicine (ACSM), 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 6379200, Fax: (317) 634-7817, http://www.acsm.org .

American Heart Association (AHA), 7272 Greenville Ave., Dallas, TX, 75231, (800) 242-8721, http://www.heart.org .

Heart Rhythm Society, 1325 G Street NW, Ste. 400, Washington, DC, 20005, (202) 464-3400, Fax: (202) 464-3401, info@HRSonline.org, http://www.hrspatients.org .

L. Lee Culvert

  This information is not a tool for self-diagnosis or a substitute for professional care.