Diagnosis of MR depends in the first instance on accurate auscultation. Usually the diagnosis can be made with reasonable certainty on these grounds alone. In some cases, DE is useful to confirm the presence of a jet of blood flowing into the LA during systole. Frequently, no evidence of gross valvular change is seen using two-dimensional echocardiography (2DE), although this does not exclude the possibility that MR is present.
Once MR has been diagnosed, it is important to consider other conditions which may cause similar clinical signs to MR. If signs such as tachypnoea and dyspnoea are present, the respiratory system should be examined further to establish whether any other disease processes are contributing to the signs. It is often particularly relevant to rule out the presence of allergic respiratory conin adults and respiratory infections in foals. Radiography, endoscopy, cytological examination of tracheal or bronchio-alveolar lavage samples and clinical pathological investigations may be appropriate if respiratory disease is considered to be a differential diagnosis or a complicating factor. If inflammatory small airway disease (COPD) is present, appropriate managemental changes should be instituted so that it does not compromise athletic performance or allow clinical signs, attributable to this condition, to become confused with signs of a deterioration in the severity of the MR at a later date.