Atrial fibrillation and a corresponding enlargement of the left atrium may cause an increase in size of the mitral valve annulus. With a sinus rhythm, the mitral annulus undergoes dynamic changes during the cardiac cycle. For example, at the end of diastole the annular area is smaller than at the end of systole.
To determine who can perform aquatic therapy, we must define what aquatic therapy is. First, notice that aquatic therapy is considered a therapeutic procedure, not a modality. There are many technical and practical distinctions between the practice of aquatic therapy and the application of therapeutic modalities.
Hydrotherapy is the use of water to provide therapeutic effects. This is quite a wide ranging topic and can include treatments such as steam rooms and clonic hydrotherapy, but in this case we are referring to the use of water (in a hydrotherapy pool) to help with musculoskeletal and neural rehabilitation, as often used in physical therapy.