Similar to the New York Heart Association (NYHA) classification of functional status, patients may move from one ACHD AP classification to another over time. If clinical status worsens, the classification will change to a higher severity group, but improvement in status, for example after an intervention such as valve replace- ment or control of arrhythmia, can result in change to a lower severity classification. Such movement among classes is unlike the AHA HF A to D classification,S2.3-17 in which patients move in only one direction. This ACHD AP classification is used throughout this document, par- ticularly when considering follow-up visits and need for testing. As the ACHD AP classification worsens because of changes in physiology (eg, development of arrhyth- mias, HF, end-organ disease), the nature and frequency of recommended follow-up visits and testing will also change, adapting to the patient s changing circum- stance instead of depending solely on a description of anatomic disease, which may not adequately discrimi- nate physiological changes that alter severity over time. Some patients with ACHD may have substantial ac- quired comorbidities unrelated to CHD and, as a conse- quence, their follow-up strategies might be more appro- priately based on other existing guidelines for acquired heart disease. For example, an 80-year-old patient who Pulmonary hypertension Pulmonary hypertension is a broad term that encompasses pulmonary arterial hypertension, which is pulmonary hypertension with increased pulmonary vascular resistance. This document defines PH and PAH as they are used in the field of pulmonary hypertension. Pulmonary hypertension is defined as: Mean PA pressure by right heart catheterization 25 mmHg. 