An experienced(!) veterinarian or animal cardiologist can usually make an initial suspicion diagnosis on a left-right shunt already after the auscultation, since the heart sounds in this case are very typical – it sounds as if 'wind blowing through a tunnel'. However, it is important that the attending vet listens close enough underneath the shoulder in order not to miss the typical heart noise. Often you can also feel a buzzing from the outside by placing your hand on the chest above the open ductus. Of course, such suspicious diagnosis must always be confirmed by means of other examination techniques.
In many cases, e.g. the amplitude of the blood pressure in the affected dog is increased (i.e., there is a high systolic and a low diastolic blood pressure value) and a very noticeable pulse occurs.
Whether the findings can be confirmed by means of an X-ray image depends on the size of the defect. The larger this defect is, the more other changes as e.g. an enlarged heart shadow, dilatation of the vessels, and the enlargement of the left atrium, as well as signs of an overflow of the lung up to the pulmonary dysfunction or even pulmonary oedema.
If there are indications for a rhythmic disturbance, an ECG is also recommended.
In addition, the typical blood flow in the pulmonary artery as well as the unclosed vessel itself can be visualized by means of heart ultrasound.
In a right-left shunt, the diagnosis is more difficult, especially by auscultation, since there is usually no cardiac noise but only a split second heart tone. There is also no typical shunt flow in the ultrasound, so that a diagnosis by means of cardiac ultrasound by means of contrast examination must be carried out with a great deal of experience on the part of the cardiologist. The course of the contrast medium is followed. If the contrast medium is detected in the aorta of the abdomen, this is the clear sign for a PDA with right-left shunt.
Further typical signs of a PDA with a right-left shunt are a blue coloration of the posterior, but not the anterior mucous membranes (differential cyanosis) and an abnormal multiplication of the blood cells (polycythemia), why the preparation of a haemogram is recommended as a diagnostic tool.