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A chest x-ray produces an image of the chest, usually in two views: anteroposterior and lateral. The anteroposterior (or more accurately posteroanterior) view is a film shot showing the chest from the front, while the lateral is a side view of the chest. In a chest x-ray, rays emitted from a machine penetrates the chest from the back going forward (in an anteroposterior view) and from on side to another (in a lateral view) to a film placed in front of or on the side of a patient. These films will show the bones, heart and blood vessels inside the chest.

An antero-posterior view of chest x-ray.  The heart, lungs and blood vessels of lungs in addition to other structures such as ribs and diaphragm could be seen.

The various structures of the heart and blood vessels could be evaluated on a chest x-ray.   RA: right atrium, RV: right ventricle, LV left ventricle.

The pulmonary blood vessels are seen as white streaks and circles within the black field which represent the air in the lung tissues.

The following information could be obtained from an x-ray film of the chest which could be valuable in evaluating the heart:

The size of the heart. A large heart could represent heart failure as the heart chambers dilate when the heart muscles fatigue. On the other hand a small heart may represent dehydration.

The contour of the heart. Enlargement of a particular chamber or blood vessel may be identified by this method of imaging.

The extent of the blood flow to the lungs could also be roughly estimated. In heart lesions such as tetralogy of Fallot where there is less blood flow to the lungs, the lung (pulmonary) vascularity is reduced. While in lesions where there is increased blood flow to the lungs such as in atrial and ventricular septal defects there will be prominence of such blood vessels on the chest x-ray.

This x-ray shows an enlarged heart as well as prominent pulmonary (lung) blood vessels as seen in patients with an atrial septal defect (ASD).  The increase in blood flow to the right atrium and right ventricle as a result of  the ASD will cause the heart to dilate.   There is also increase in blood flow o the lungs causing them to be engorged and more visible on the chest x-ray.

Although a chest x-ray is a crude method in evaluating the heart, it is still a very valuable tool. It provides information not possible to obtain from examining the patient. It may not provide the detailed information of an ultrasound image of the heart (echocardiogram), however, it continues to be used because of its cheap cost.
Is it harmful?

Exposure to radiation including x-ray is always something to be concerned about. However, the amount of radiation in a chest x-ray is miniscule and few films a year does not amount to any danger. Nevertheless, it should be (as in any medical test) be ordered only when valuable information is sought, not otherwise available through more simple and safer means.


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