WHO functional classes
| WHO Functional Class | Description |
| Class I | Can perform ordinary physical activity without symptoms. |
| Class II | Ordinary activity causes symptoms of dyspnea, fatigue, chest pain or near syncope. Comfortable at rest. |
| Class III | Marked limitation of activity. Less than ordinary activity causes symptoms. Comfortable at rest. |
| Class IV | Cannot perform any activity without symptoms. Dyspnea and/or fatigue at rest. |