4.3.1 Plain radiography
Satisfactory radiography of the entire adult chest requires high output radioequipment which is not widely available in practice. Only lateral views are feasible in the adult; four separate radiographs are usually needed to show all the lung fields and even the cardiac silhouette cannot be included on one film. Radiographs may provide some useful information about pulmonary disease which may be relevant in animals with suspected cardiac disease, but thoracic radiographs must be of high quality to avoid over-interpretation and experience is required to distinguish the subtle indicators of disease from the wide range of normality. Pulmonary oedema may result in an interstitial pattem and in some cases an alveolar pattern; however, a number of other conditions have a similar radiographic appearance. Very limited information about heart chamber size can be obtained and radiography is therefore of very limited value in evaluation of animals with suspected cardiac disease.
Adequate quality radiographs of the thorax of foals can be taken with many portable X-ray machines. However, radiographs in foals are of limited value for assessment of cardiomegaly, which must be marked to result in a reliable, detectable degree of tracheal elevation and increased sternal contact. Severe cardiac disease may result in changes in the pulmonary vessels or cause puloedema. Radiographs are more valuable for identifying some pulmondiseases. Conditions such as pneumonia may result in clinical signs which could be confused with those of cardiac insufficiency, or may complicate clinical signs in animals in which significant cardiac disease is present.