(v) What tests can be performed to understand the degree of development of pulmonary hypertension? In patients with left-to-right shunt congenital heart disease combined with pulmonary hypertension, the key to the success or failure of surgery and long-term outcome is the correct assessment of the degree of pulmonary vascular disease and its reproducibility. Clinical considerations are usually based on the patient’s age, medical history, arterial oxygen saturation, physical signs such as the second pulmonary artery sound and murmur intensity, as well as electrocardiogram, X-ray chest radiograph and echocardiogram data. Age is an important factor. Infancy (within 2 years of age) is the period of fastest development of alveoli and intra-alveolar arteries. If children with combined pulmonary hypertension can be treated during this period, their prognosis is significantly better than that of adult patients with equivalent pulmonary vascular lesions, because the development of pulmonary vessels has not yet been completed, with the reversal of the original lesion vessels and the growth of new vessels after surgery. Li Pingyuan, Department of Pediatric Cardiac Surgery, Fu Wai Hospital, Beijing, China Currently, right heart catheterization plus oxygen inhalation test is the main clinical tool to determine the degree of pulmonary hypertension lesions and to determine the indications for surgery. Oxygen inhalation test is important for evaluating pulmonary hypertension. A significant decrease in pulmonary artery pressure or resistance after inhalation of pure oxygen often indicates a large proportion of dynamic factors. Due to the method and operation of right heart catheterization, such as when the child is under deep sedation or anesthesia, polycythemia or combined pulmonary disease, the results sometimes have more obvious errors, so the results of right heart catheterization should be interpreted in combination with clinical manifestations and other data. In addition, because of the rapid developmental changes in the pediatric cardiovascular system, cardiac catheterization data must be combined with the age of the child. Conventional oxygenation tests for screening surgical indications have some clinical significance for mild and moderate pulmonary hypertension and lack sensitivity for moderate and severe pulmonary hypertension. In order to keep patients with a critical degree of pulmonary vascular disease from losing their last chance for surgery, and to control surgical mortality, there has been a clinical search for safe, reliable, sensitive and non-invasive or less invasive methods. In addition to clinical manifestations, a number of tests are pivotal in the assessment of pulmonary hypertension. These include: (1), transcutaneous oxygen saturation (SpO2) or arterial oxygen saturation (SaO2): as pulmonary hypertension progresses, pulmonary blood decreases significantly and so does the oxygen intake. Oximetry provides a visual representation of the amount of oxygen in the blood and is easy to measure. Generally speaking, patients with oxygen saturation over 95% can mostly receive corrective surgery for precordial disease; if it is below 90% or even below 85%, the chances of surgery are slim. (2), Chest X-ray: Chest X-ray is essential to assess the degree of development of pulmonary hypertension. Through chest radiographs, the degree of development of pulmonary artery lesions can be roughly grasped and the feasibility and clinical outcome of surgery can be predicted. Although there is a lack of quantitative objective criteria, experienced physicians attach more importance to chest radiographs than even right heart catheterization. (3), ECG: Patients with pulmonary hypertension will present with typical ECG manifestations (e.g. pulmonary P waves). More importantly, the ECG can reflect right and left ventricular hypertrophy. If the patient has predominantly left ventricular hypertrophy, it often suggests that the procedure can be performed safely; whereas if the patient has biventricular hypertrophy or even predominantly right ventricular hypertrophy, the safety of the procedure will be greatly compromised. (4) Echocardiography: Echocardiography is the most important test to confirm the diagnosis of precordial disease and pulmonary hypertension, and is the basic basis for clinical diagnosis. If echocardiography suggests that the type of precordial disease originally with left-to-right shunt evolves into bidirectional shunt or even right-to-left shunt, it means that the patient has developed severe pulmonary hypertension. It is important to note, however, that even if the direction of the shunt has changed, this does not mean that the patient is completely lost to surgery (although this is true in most patients), and relying on ultrasound findings alone may deprive the patient of the last chance for corrective treatment. (5) Right heart catheterization and rapid pulmonary artery dilation test: Right heart catheterization is by far the most objective, effective, and authoritative means of assessing pulmonary hypertension. Through right heart catheterization, the patient’s pulmonary artery pressure, body/pulmonary circulation blood volume and pulmonary artery resistance can be accurately measured. Among them, pulmonary artery resistance is the key data to determine whether the patient can be operated. The so-called rapid pulmonary artery dilation test is done after adequate oxygenation or inhalation of pulmonary artery dilation drugs, followed by completion of right heart catheterization. The purpose is to discard the interference of functional factors such as pulmonary artery spasm and to more accurately measure the extent of disease development in the pulmonary vasculature itself. Therefore, we recommend that all children(s) with pulmonary hypertension undergo standardized right heart catheterization and rapid pulmonary artery dilation tests. This test should be performed in patients with precordial disease combined with pulmonary hypertension, even if it is inoperable, so that the current progression of pulmonary hypertension can be grasped and used as a standard for clinical guidance of drug therapy, creating a ray of hope for improvement of the patient’s condition.