Dr. Prabhat AryaMD · Internal Medicine
ConditionsKnow your condition

Your ECG report, line by line.

Most ECGs that say “abnormal” or “borderline” belong to healthy hearts. Here is what each printed line means, and the few that need a doctor soon.

Reviewed by Dr. Prabhat Arya, MBBS, MD (Internal Medicine)

Reviewed · Next review · Sources: NHS, MedlinePlus, British Heart Foundation

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Read this first.

An ECG is a ten-second recording of the heart’s electrical signals. The top lines are measurements; the bottom line is the machine’s own reading. That machine reading is written by a computer program, not a doctor, and it is cautious: it flags anything slightly unusual, so “abnormal ECG” or “borderline ECG” is printed on many normal hearts.

An ECG is read together with how you feel. The same line means one thing in a fit 30-year-old with no symptoms and another in a 60-year-old smoker with chest tightness on walking. Typical ranges below are for adults; go by the range printed on your own report where it gives one.

The most useful thing you can do is compare with an old ECG. A finding that was there five years ago and has not changed is far less worrying than a new one. Keep every ECG you have ever had, including the paper strip.

A normal ECG at rest does not rule out narrowed heart arteries: many people with angina have a normal resting ECG. If you get chest discomfort or breathlessness on walking that settles with rest, see a doctor this week even if your ECG was normal.

Every value, one by one.

Heart rate (Vent. rate, HR)

Beats per minute while you lie still for the recording

Typical adult range 60–100 bpm (50–60 is common and normal in fit people and during rest)

High usually means
Above 100 is called sinus tachycardia when the rhythm is otherwise normal. Usually nervousness at the test, fever, dehydration, pain, anaemia, an overactive thyroid, caffeine, smoking or some cough syrups and inhalers.
Low usually means
Below 60 is called sinus bradycardia. Very common in fit people, young adults, during sleep and in people taking BP or heart medicines such as beta-blockers. An underactive thyroid can also slow the heart.
Usually nothing to worry about when
The rate is 50–60 and you feel well, or it is 100–110 and you were anxious, had fever or had just climbed stairs to the lab.
See a doctor when
See a doctor within a few days if your resting rate stays above 110 or below 50 on repeat checks, or sooner (today) if a slow or fast rate comes with dizziness, fainting, chest pain or breathlessness.

PR interval

The time the signal takes to travel from the top chambers to the bottom chambers

Typical adult range 120–200 ms

High usually means
Over 200 ms is called first-degree AV block. Despite the name, nothing is blocked: the signal is only a little slow. Common in fit people and older adults, and with some BP and heart medicines (beta-blockers, some calcium channel blockers, digoxin).
Low usually means
Under 120 ms is usually a normal variant. Rarely it is from an extra electrical pathway; the report will then say WPW or pre-excitation or “delta wave”.
Usually nothing to worry about when
A long PR on its own, with a normal heart rate and no dizziness or fainting.
See a doctor when
See a doctor within a week or two if the report says WPW or pre-excitation, or if a long PR comes with a slow pulse or dizzy spells. See a doctor today if you have fainted.

QRS duration

How long the main pumping chambers take to switch on

Typical adult range Under 120 ms (often 80–110 ms)

High usually means
120 ms or more usually means a bundle branch block (see below). 110–120 ms is often printed as “incomplete” block or “intraventricular conduction delay” and is usually harmless.
Usually nothing to worry about when
It is under 120 ms, or slightly above 110 ms with no other change.
See a doctor when
A new QRS of 120 ms or more, especially with breathlessness or swollen feet, needs a doctor within a week or two for a heart scan (echo).

QT / QTc

How long the heart takes to recharge after each beat; QTc is QT corrected for heart rate

Typical adult range QTc up to about 450 ms in men and 460 ms in women

High usually means
A long QTc is most often from medicines (some antibiotics such as azithromycin and levofloxacin, some anti-sickness, antifungal, malaria and mental-health medicines), low potassium, magnesium or calcium, or an underactive thyroid. A few people are born with it. The machine also over-measures QTc when the heart is fast.
Usually nothing to worry about when
It is just above the line (for example 455–470 ms) on one ECG, you take none of those medicines and you have never fainted. A repeat ECG and a potassium check are enough.
See a doctor when
See a doctor within a day or two if QTc is 500 ms or more, or if it is long and you are taking any of the medicines above; take the list of medicines with you. Fainting with a long QTc needs hospital today.

Axis (left or right axis deviation)

The overall direction of the heart’s electrical signal, in degrees

Typical adult range −30° to +90°

High usually means
Above +90° is right axis deviation. Common and normal in young, slim people; sometimes from long-standing lung disease.
Low usually means
Below −30° is left axis deviation. Often from a harmless slow branch of the wiring (printed as “left anterior fascicular block”), being overweight, or a thickened heart muscle from high BP.
Usually nothing to worry about when
It is the only finding and you have no symptoms. Axis deviation alone is rarely a reason to worry.
See a doctor when
Raise it at your next check-up if you also have high BP, breathlessness or another ECG finding; the doctor may ask for an echo.

Sinus rhythm

The heart’s own natural pacemaker is in charge

What it means
This is normal. “Normal sinus rhythm” is the healthy pattern. “Sinus bradycardia” and “sinus tachycardia” mean the same normal rhythm, only slower or faster than 60–100 (see heart rate).
Usually nothing to worry about when
Always, on its own.
See a doctor when
Not needed for this line.

Sinus arrhythmia

The heart speeds up slightly as you breathe in and slows as you breathe out

What it means
A normal pattern, strongest in young and fit people. It is a sign of a healthy nervous system, not a heart problem.
Usually nothing to worry about when
Always, when the report calls it sinus arrhythmia.
See a doctor when
Not needed for this line.

Ectopic beats (VPC, VPB, PVC, APC, APB)

Extra early beats from the lower (ventricular) or upper (atrial) chambers

What it means
Most people have some extra beats every day. They feel like a skipped or thumping beat. Caffeine, tea, lack of sleep, stress, alcohol, smoking and low potassium make them more frequent.
Usually nothing to worry about when
One or two on the strip, in someone who feels well and has no known heart disease.
See a doctor when
See a doctor within a few weeks if they are frequent (many on a ten-second strip), come in runs, or you have known heart disease; a 24-hour recording (Holter) and echo may be advised. Today if they come with fainting or chest pain.

Atrial fibrillation (AF) or atrial flutter

The top chambers quiver instead of beating; the pulse is irregular

What it means
A common rhythm problem, more so after 60 and with high BP, thyroid problems, alcohol or valve disease. Its main danger is a clot that can cause a stroke, which treatment greatly reduces.
Usually nothing to worry about when
Never ignore a first finding of AF, even without symptoms.
See a doctor when
See a doctor within a few days if AF is new, to check the cause and decide on clot-preventing treatment. Go to hospital today if it comes with chest pain, breathlessness, fainting or a heart rate above about 120.

Right bundle branch block (RBBB), complete or incomplete

The signal reaches the right pumping chamber a little late

What it means
Common, and in most people harmless, especially “incomplete RBBB”, which is often a normal variant. Complete RBBB becomes more common with age; sometimes it goes with lung disease or a hole in the heart wall from birth.
Usually nothing to worry about when
It was there on an older ECG, or you are well with no breathlessness, chest pain or fainting.
See a doctor when
Mention a new complete RBBB at your next check-up; an echo may be advised. Go to hospital now if it is new and comes with chest pain or sudden breathlessness.

Left bundle branch block (LBBB)

The signal reaches the main left pumping chamber late

What it means
Unlike RBBB, LBBB usually points to something in the heart muscle: long-standing high BP, narrowed heart arteries, a weak heart muscle or valve disease. It also hides other ECG signs, so the ECG cannot be read normally.
Usually nothing to worry about when
It is known, unchanged from older ECGs, and you have already had an echo.
See a doctor when
A new LBBB needs a doctor within a week or two for an echo and a heart check. With chest pain, breathlessness or fainting, go to hospital now.

LVH (left ventricular hypertrophy) or “LVH by voltage criteria”

Tall waves suggesting a thickened main pumping chamber

What it means
The machine prints “LVH by voltage” whenever the waves are tall. In young, slim people and athletes the waves are tall simply because the heart is close to the chest wall, so this is often a false alarm. True LVH is most often from years of high BP, and sometimes from a tight valve.
Usually nothing to worry about when
You are young and slim, your BP is normal, and the report says voltage criteria only, with no ST or T changes.
See a doctor when
Have your BP checked properly this month, and ask about an echo, which shows whether the wall really is thick. With LVH plus ST-T changes, or breathlessness, see a doctor within a week or two.

Early repolarisation

A slight raised start to the ST segment

What it means
A common normal pattern, especially in young men, athletes and people of African background. It looks a little like the changes of a heart attack, which is why the machine mentions it.
Usually nothing to worry about when
You have no chest pain and the pattern is the same as on older ECGs.
See a doctor when
If you have chest pain now, go to hospital now or call 112: the machine cannot always tell this pattern from a heart attack. If you have fainted, or a close relative died suddenly young, see a doctor within a few days.

Non-specific ST-T changes (ST-T abnormality, T wave flattening)

Small changes in the recovery part of each beat that point to no particular cause

What it means
The most common line on Indian ECG reports. “Non-specific” means the change does not point to any disease. Usual causes: position of the electrodes, breathing fast or anxiety during the test, a meal just before, being overweight, low potassium, BP medicines, and simply being a woman (more common in women). Occasionally it is an early sign of reduced blood flow to the heart.
Usually nothing to worry about when
You have no chest discomfort, breathlessness on walking or fainting, and the change is small or the same as on an older ECG.
See a doctor when
See a doctor within a week or two if you have diabetes, high BP, high cholesterol, you smoke, a parent had early heart disease, or you get chest tightness or breathlessness on exertion: a treadmill test or echo may be advised. If you have chest pain now, go to hospital now or call 112.

T wave inversion

The recovery wave points down instead of up

What it means
In some leads it is normal: aVR always, and often lead III and V1. In V2 and V3 it is normal in children and sometimes stays into adult life, but in an adult it should be looked at by a doctor. In other leads it can be from high BP, a thick heart muscle, a past or current lack of blood flow, or a recent viral illness.
Usually nothing to worry about when
It is only in the leads named above and you are well, or it is unchanged from an old ECG.
See a doctor when
New T wave inversion across several chest leads needs a doctor within a few days, or today if you have had chest pain in the past few days. With chest pain now, go to hospital now.

Poor R wave progression

The upward wave grows less than expected across the chest leads

What it means
Most often from electrodes placed a little high or low, being overweight, large breasts, or lung disease. Occasionally it is a sign of an old heart attack at the front of the heart.
Usually nothing to worry about when
You have no symptoms and no heart risk factors; a repeat ECG with careful electrode placement often looks normal.
See a doctor when
If you have diabetes, high BP, smoke or have had chest pain, ask for an echo within a few weeks.

Q waves, “septal infarct, age undetermined” or “possible old MI”

The machine guessing at an old heart attack

What it means
The machine prints this often, and is often wrong: electrode position, body shape and normal small Q waves all set it off. When it is real, it means a heart attack in the past, sometimes one that went unnoticed (more likely in people with diabetes).
Usually nothing to worry about when
A doctor has looked at the actual tracing and is not concerned, or older ECGs show the same.
See a doctor when
See a doctor within a week or two to have the tracing read and, if needed, an echo. Do not panic over the machine’s words alone.

Low voltage QRS

Waves smaller than usual in all leads

What it means
Usually from being overweight, lung disease (COPD) or swelling, which damp the signal. Rarely from fluid around the heart or a very underactive thyroid.
Usually nothing to worry about when
You are overweight or have known COPD and feel as usual.
See a doctor when
See a doctor within a few days if you are newly breathless, have swollen legs or feel your heart pounding.

“Abnormal ECG”, “Borderline ECG” or “Unconfirmed report”

The machine’s summary line at the top or bottom

What it means
A computer’s first guess, made before any doctor looks. It labels any single small finding (a heart rate of 58, a slightly long PR) as abnormal or borderline. “Unconfirmed” means no doctor has checked it yet.
Usually nothing to worry about when
The only findings are ones this page calls harmless, and you have no symptoms.
See a doctor when
Have the tracing read by a doctor within a week or two if you cannot match the line to one of the harmless findings above, or sooner if you have symptoms.

Results that go together.

PatternsTypical, not certain
When you seeIt usually means
Sinus bradycardia with first-degree AV blockCommon in fit people and in people on beta-blockers. Usually harmless if you never feel dizzy or faint.
Sinus tachycardia with flat T waves during fever or vomitingUsually the illness itself, dehydration or low potassium. Repeat the ECG once you are well.
LVH with ST-T changes (“LVH with strain”) and high BPUsually years of high BP thickening the heart. Needs an echo and properly controlled BP; see a doctor within a week or two.
Long QTc with low potassium or a new antibioticOften settles once potassium is corrected or the medicine is changed. Check potassium and show the doctor every medicine you take.
Left axis deviation with RBBB (“bifascicular block”)Two branches of the wiring are slow. Usually stable for years, but dizziness or fainting with this pattern needs a doctor the same day.

Get help today if

  • Chest pain, pressure or tightness lasting more than 15 minutes, especially with sweating, breathlessness or pain going to the arm or jaw: call 112 or go to hospital now. Do not wait for an ECG or its report; see chest pain.
  • An ECG that a doctor or the report calls “acute MI”, “ST elevation” or “STEMI”: go to a hospital with a cath lab now, or call 112.
  • Fainting, or nearly fainting, with a pulse below 40 or above 150, or with a report of complete heart block, long QTc or WPW: go to hospital now, or call 112.
  • A report that says complete heart block, third-degree AV block, Mobitz II or 2:1 AV block: see a doctor today, even if you feel well.
  • Atrial fibrillation with chest pain, breathlessness at rest or sudden weakness of one side of the face or body: call 112.

Call 112 or go to the nearest emergency department. Ambulance: 108 (102 in some states).

Read more.

Questions people ask.

  1. Is “non-specific ST-T changes” on an ECG dangerous?

    Usually not. It is the most common line on ECG reports and is often caused by electrode position, anxiety, a recent meal or BP medicines. It matters more if you have chest discomfort on walking, diabetes, high BP, high cholesterol or smoke: then see a doctor within a week or two, who may advise a treadmill test or echo.

  2. My ECG says “abnormal” but I feel fine. Should I worry?

    The “abnormal” or “borderline” line is printed by the machine for any small finding, such as a heart rate of 58. Most such ECGs belong to healthy hearts. Have a doctor read the tracing itself and compare it with an older ECG.

  3. Does a normal ECG mean my heart is healthy?

    It means there is no sign of a problem at the moment of recording. It cannot rule out narrowed heart arteries, which often show only during exercise. Chest discomfort or breathlessness on exertion still needs a doctor this week.

  4. What does sinus bradycardia mean?

    The heart’s natural pacemaker is working normally, just slower than 60 beats a minute. It is common in fit people, during rest and with some BP medicines. It matters only if the rate is below about 50 with dizziness, fainting or tiredness, or if you have an underactive thyroid.

Where this can be checked

These are trusted general sources. The advice on this page is Dr. Arya’s, written for patients in India. Ranges differ between labs: go by the range printed on your own report.

Your whole report, read by your doctor.

Send every page, old reports too. He reads them himself and tells you what changed and what to do.

Send your report for ₹199

Dr. Prabhat Arya · MBBS, MD (Internal Medicine)