Enlarged heart seen by chance on a chest X-ray

What the report is measuring

On a chest X-ray the widest part of the heart shadow is compared with the widest part of the chest. This is the cardiothoracic ratio. A ratio above 50% (0.5) is generally judged as an enlarged heart. (Tomita 2015)(Monfared 2015) The standard X-ray for this is taken from the back (a PA view) with a deep breath in. (Monfared 2015)

Why the heart can look larger than it is

X-ray position: X-rays taken from the front (AP view), such as portable films done in bed, gave a higher ratio than CT of the same people, by 0.075 on average. The authors suggest a cutoff of 0.60 rather than 0.50 for these films. (Sahin 2019)
Breathing: in a CT study, the heart measured larger and the ratio was higher when people had breathed out than when they had breathed in. (Tomita 2015)
Matching the echocardiogram: after a heart attack, 56% of people whose X-ray showed a large heart had one on an echocardiogram, and the authors suggest calling it an enlarged heart shadow rather than true cardiomegaly. (McKee 2017)

How well the X-ray matches a heart ultrasound

Large heart shadow on a chest X-ray compared with an echocardiogram (study results, simplified)
Study	What it found
Review of 6 studies, 466 people	Picked up 83.3% of enlarged main pumping chambers, but only 43.5% of large shadows were a true enlargement; a normal shadow was correct 82.7% of the time
244 people after a heart attack	56% of large shadows were confirmed; the X-ray missed 60% of hearts that were enlarged on the echocardiogram
AP (front) X-rays, 130 people	At a 0.50 cutoff, 32% specificity; at 0.60, 92% specificity

Sources: (Loomba 2015)(McKee 2017)(Sahin 2019)

What usually comes next

Your doctor asks about symptoms and examines you. NICE says to take a history and examine the person to confirm or rule out heart failure. (NICE NG106)
A blood test (NT-proBNP) if heart failure is suspected. NICE says: above 2,000 ng/L, refer urgently for specialist assessment and an echocardiogram within 2 weeks; 400 to 2,000 ng/L, within 6 weeks; below 400 ng/L in someone not on treatment makes heart failure less likely. (NICE NG106) MedlinePlus lists a BNP blood test and an echocardiogram among the tests for heart failure. (MedlinePlus)
An echocardiogram (a heart ultrasound) checks the valves and how well the main pumping chamber works. (NICE NG106)
Other tests: NICE lists an ECG, and considers a chest X-ray, blood and urine tests and breathing tests to look for other causes. (NICE NG106) The NHS lists the same kinds of tests and says you may be referred to a heart specialist. (NHS)

The same scan may show other findings with their own pages: aortic valve calcium, heart artery calcium and a wide chest aorta.

How it ties to blood pressure checks

The NHS lists long-term strain from high blood pressure as a cause of heart failure. (NHS) The USPSTF calls high blood pressure a major risk factor for heart failure and recommends screening all adults 18 or older (grade A): every year from 40 or with higher risk, and every 3 to 5 years at 18 to 39 after a normal reading. (USPSTF 2021) See blood pressure readings: what they mean.

Who it applies to

Adults told their chest X-ray shows a large heart shadow. The NHS says anyone can get heart failure, with higher risk at 65 or older. (NHS) If you already know you have heart failure, see screenings if you have heart failure. If a close relative has cardiomyopathy, see heart screening if a relative has cardiomyopathy.

NHS, when to get help for possible heart failure symptoms: (NHS)

See a GP if:

you have symptoms of heart failure

Ask for an urgent GP appointment or get help from NHS 111 if:

you feel breathless when lying down or from everyday activity
you're coughing up frothy pink phlegm
you have suddenly gained weight

Call 999 if:

you're having severe difficulty breathing (you're gasping, choking or not able to get words out)
your lips or skin are pale, blue or grey
someone has passed out and is not responding normally

In the US, the emergency number is 911.

Routine age-based screening

A finding on an X-ray does not replace the routine screenings for your age. See heart screenings by age.

Where they differ:

Whether the X-ray alone leads to an echocardiogram. NICE starts from suspected heart failure: history, examination and an NT-proBNP level decide referral, and lists a chest X-ray only as an extra test. (NICE NG106) A New Zealand study after heart attacks concluded that everyone with a large heart on the X-ray should have an echocardiogram. (McKee 2017)
The cutoff. A ratio above 0.50 is the usual definition. (Tomita 2015) For X-rays taken from the front, one study suggests 0.60. (Sahin 2019)
What the word means. Reports often say "cardiomegaly", while the New Zealand authors suggest reporting the ratio and calling it an enlarged heart shadow. (McKee 2017)

Your doctor decides what your result means for you.

Questions people ask

Does a large heart on a chest X-ray mean my heart is enlarged?

Not always. In a review of 6 studies, fewer than half of the people with a large heart shadow on an X-ray had an enlarged main pumping chamber on an echocardiogram. A normal-looking heart on an X-ray more often matched a normal echocardiogram. (Loomba 2015)

Why can the X-ray make the heart look bigger?

An X-ray taken from the front (often done in bed or on a ward) makes the heart look larger than the standard X-ray taken from the back. The heart and the heart to chest ratio also measure larger when the lungs are less full of air. (Sahin 2019) (Tomita 2015) (Monfared 2015)

What test usually comes next?

If heart failure is suspected, NICE says to measure a blood test called NT-proBNP, and to refer for an echocardiogram (a heart ultrasound) based on the level. Your doctor decides. (NICE NG106)

How does this link to blood pressure checks?

The USPSTF calls high blood pressure a major risk factor for heart failure and recommends blood pressure screening for all adults, every year from age 40. (USPSTF 2021)

Is it more common with age?

The NHS and MedlinePlus both say the risk of heart failure is higher at 65 or older. (NHS) (MedlinePlus)