April 6, 2020

How To Read An Electrocardiogram (EKG/ECG)

Healthcare professional reading EKG information on patient

Updated: 4/6/2020

Regular, irregular, fast, slow, wide, narrow, stable, unstable. Does looking at a 12-lead EKG put your own heart into a lethal rhythm? Nurses are usually the first ones to read that “hot off the press” EKG tracing. A 12-lead EKG is considered the gold standard; however, a 4 lead EKG can also diagnose different heart conditions. 

This article has been reviewed by our panel of experienced registered nurses:

  • Tyler Faust, MSN, RN
  • Chaunie Brusie, BSN, RN
  • Kathleen Coduvell Gaines, BSN, RN, BA, CBC

What is an EKG?

Before interpreting an EKG it is important to know what an EKG is and its importance. An EKG is a representation of the electrical activity of the heart muscle as it changes with time, usually printed on paper for easier analysis. The EKG is a printed capture of a brief moment in time. 

EKGs can be used to diagnose heart attacks, heart problems including electrical malfunctioning and other heart problems. They are often used to diagnose heart problems in combination with an echocardiogram, or echo.

>> Related: How to Become an EKG Technician

7 Steps to Reading an EKG/ECG

How do you know when you need to act immediately or can wait for expert consultation? Here are seven tips to help you gain confidence in interpreting what you see.

1. Assess Your Patient

This must come first! There are many clues you can learn when obtaining the EKG that will help you analyze and act on what you see.

  • Is the patient’s skin warm and dry, or is it damp and clammy?
  • How is their color?
  • Are they having chest pain?
  • Can you palpate peripheral pulses?
  • Is your patient talking to you or are they struggling to catch their breath?
  • What is their capillary refill?
  • Do they have underlying heart conditions?
  • What is their baseline physical activity?
  • Have they ever had an EKG before?
  • Have they ever been diagnosed with a heart condition?

Looking at a sheet of paper with a tracing on it does not provide enough information. A heart rate of 38 can be normal in an athlete.¹ But it also can require an immediate pacemaker insertion if accompanied by chest pain, shortness of breath, and an EKG interpretation of third degree heart block.²

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2. Know Your Normals

Don’t sweat all the complex details when you are first beginning to read and interpret EKGs. A normal heart rhythm contains a P wave, a QRS, and a T wave.³ Knowing the normal amplitude, deflection, and duration of each component is essential to accurate rhythm and EKG interpretation.

  • Amplitude: This measures the voltage of the beat and is determined by how high the wave reaches, as measured by each square vertically on the chart. 10 mm = 1 mv. 5 squares = .5 mV and 2.5 squares = .25 mV
  • Deflection: Which lead on the patient it’s coming from
  • Duration: How long it is, as measured by squares going horizontal⁴

What’s a normal adult heart rate?

  • Normal = 60 – 100 bpm
  • Tachycardia > 100 bpm
  • Bradycardia < 60 bpm

 Infographic demonstrating how to read EKG chart

Normal 12-Lead EKG/ECG Values

Wave/Interval Values
P Wave Amplitude: 2-2.5 mm high (Or 2.5 squares)
Deflection: + in I, II, AVF, V2-V6
Duration: 0.06 - 0.12 sec
PR Interval Duration: 0.012 - 0.20 sec
QRS Complex Amplitude: 5-30 mm high
Deflection: + in I, II, III, AVL, AVF, V4-V6
Duration: 0.06 - 0.10 sec
ST Segment Duration: 0.08 - 0.12 sec
T Wave Amplitude: 0.5 mm in limb leads
Deflection: I, II, V3-V6
Duration: 0.1 - 0.25 sec (Or greater)
QT Interval Duration: 0.36 - 0.44 sec


Leads and Heart View

Lead Heart View
Inferior II, III, AVF
Lateral I, AVL, V5, V6
Anterior V2, V3, V4
Right atrium and cavity of left ventricle V1 and AVR

The twelve leads show the electrical current through the heart from different planes.  Think of each lead as a different snapshot of the heart you are trying to interpret.  

There are six limb (I, II, III, AVR, AVL, AVF) leads and six precordial (V1-V6) leads.  The limb leads look at the heart from a vertical perspective; the V leads show a horizontal perspective.  

Keeping this in mind will help you to interpret what you are seeing and identify which areas of the heart may be “hurting” or have damage.  

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3. Use a Systematic Approach

Approach your analysis to a 12 lead EKG the same way every time. 

First, determine rate, and if any tachycardia (more than 100 beats/minute) or bradycardia is present (less than 60 beats/minute).  Next, determine whether your rhythm is regular or irregular; you can use calipers if you have them or use a simple piece of paper and track your P waves and QRS complexes with a pencil mark and see if they march along or have gaps. 

First, determine whether your rhythm is regular or irregular; you can use calipers if you have them or use a simple piece of paper and track your P waves and QRS complexes with a pencil mark and see if they march along or have gaps. 

After determining this, next decide if your rhythm is fast or slow, irregular or regular (more on this in the next section).  

Lastly, examine the ST segments for any elevation or depression; again, you can use a sheet of paper to help you evaluate this.  If you can tell elevation or depression without the help of paper, be prepared to act and inform the provider immediately. 

4. Determine Your Heart Rate 

Look at the EKG to see if the rate is regular and how fast the heart is beating; both are important for rhythm interpretation. The pace at which a rhythm is conducting can help determine the stability of the rhythm.  A stable rhythm often correlates with a stable patient.  Slow or fast can be “good” or “bad” depending on the patient presentation and corresponding rhythm.  

Rate is usually determined by which electrical circuit is “conducting” the heart.  Rhythms conducted above the atria are usually above 60 and tend to be abnormal when the rate is fast (atrial flutter, atrial fibrillation, supraventricular tachycardia).  Rhythms conducted below the atria are slower and tend to be unstable when the rate is irregular (heart blocks). 

Another comment about rate: know what medications your patient is taking. Many heart medications have beta-adrenergic effects which correlate to slower heart rates  such as beta blockers.    

It is important to determine if a heart rate is regular or irregular. A regular heart rhythm has all of the aspects previously discussed. 

Irregular rhythms can be either:

  • Regularly irregular (i.e. a recurrent pattern of irregularity)
  • Irregularly irregular (i.e. completely disorganised)

In order to determine if a rhythm is regular, mark out several consecutive R-R intervals on a piece of paper, then move them along the rhythm strip to check if the subsequent intervals are the same.

5. Identify Lethal Rhythms

When evaluating lethal rhythms on a 12 lead EKG, it is important to remember the rhythm alone can be lethal as well as what the EKG is showing you in terms of heart function.  

A rhythm that does not perfuse well can lead to impending heart failure quickly if not addressed.  

Some dangerous heart rhythms are: 

  • Mobitz Type II (Type 2 Heart Block)
  • Third Degree Heart Block
  • Ventricular Tachycardia
  • Idioventricular Rhythms

Other potentially concerning heart rhythms are:

  • Atrial Fibrillation 
  • Atrial Flutter 
  • Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
  • Atrioventricular Reentrant Tachycardia (AVRT) 
  • Ectopic Atrial Rhythms 
  • First-Degree Atrioventricular (AV) Block 
  • Junctional Rhythms 
  • Multifocal Atrial Tachycardia (MAT) 
  • Second-Degree Atrioventricular (AV) Block Type I (Wenkebach) 
  • Second-Degree Atrioventricular (AV) Block Type II E
  • Third-Degree Atrioventricular (AV) Block 
  • Ventricular Tachycardia (VT)
  • Wandering Atrial Pacemaker (WAP) 
  • Bifascicular Block 
  • Left Anterior Fascicular Block (LAFB) 
  • Left Atrial Enlargement (LAE) 
  • Left Bundle Branch Block (LBBB) 
  • Left Posterior Fascicular Block (LPFB) 
  • Left Ventricular Hypertrophy (LVH) 
  • Poor R Wave Progression 
  • Right Atrial Enlargement (RAE) 
  • Right Bundle Branch Block (RBBB) 
  • Right Ventricular Hypertrophy (RVH) 
  • Trifascicular Block 

When it comes to heart function, the view (lead) you are looking at will determine which part of the heart you are trying to interpret. This is especially important when analyzing ST segment abnormalities. The location of the infarct determines what treatment should be used to improve oxygenation to the heart to minimize damage.  

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6. Access Your Resources

There are many awesome resources available for review, as well as practice EKG tracings to perfect your skills.  

The more familiar you are with different rhythms, the easier interpretation becomes.  Don’t forget your colleagues are great resources as well; let them know you are working on your 12 lead EKG interpretation skills and ask them to save interesting tracings for your review.  

A favorite EKG interpretation resource is ECG Interpretation Made Incredibly Easy. I also really like websites that let you practice rhythm strips and EKG interpretation for free like

7. Look at Your Patient

Yes, this is a repeat, but it is an important repetition. The most stable looking rhythm can be lethal if it doesn’t match what your patient is telling you.  And if your EKG findings are in complete disconnect from what you are seeing with your patient, you should also double-check your leads to make sure they are on correctly, have not come loose, or have any disturbance, as correct lead placement is critical to accurate interpretation.  

Trust your gut; nurses have great intuition skills—don’t be afraid to ask questions and seek more information when you feel something isn’t right. 

Carry This Card On Your Badge For Help

We like this EKG Ruler Vertical Badge ID Card Pocket Reference Guide ECG and many of our nurse friends do, too! It includes an overview of EKGs, basic terminology, and an EKG ruler.

This section includes affiliate links. 

Jobs Requiring EKG/ECG Proficiency

EKG/ECG proficiency is required for many nursing jobs.  Telemetry, cardiac, and stepdown units all require some level of proficiency.  Nurses interested in working in the intensive care unit or cardiac care unit are required to be proficient in reading EKGs. These jobs are also in high-demand.

Or perhaps you are ready to take the next step in your nursing career through an RN to BSN or RN to MSN program. Use our search tool to find the right program in your area.

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Dawn Gray, RN has been a nurse since 1987 and has spent the majority of her career in critical care and emergency department settings. She contributed several chapters to Fast Facts for the Triage Nurse, published in 2015 by Springer Publishing. Dawn loves facing a challenging shift and problem-solving difficult situations, and helping other nurses to improve quality outcomes in-patient care.

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