Final answer:
The mitral valve is most commonly affected in rheumatic heart disease, leading to mitral regurgitation and insufficiency.
Step-by-step explanation:
The valve most often affected in patients with rheumatic heart disease is the mitral valve. Rheumatic heart disease can lead to various issues, including mitral regurgitation, which is the most common type of valve disorder.
This disease is an autoimmune reaction that typically follows rheumatic fever, and is marked by inflammation and scarring of the heart valves, leading to their malfunction. Such malfunctions can result in disruptions to normal blood flow, commonly leading to insufficiencies named after the affected valve, like mitral insufficiency.