Heart disorders can limit a person's ability to perform physical activities. One way to evaluate the severity of a heart disorder is to determine how limited this ability is.

Doctors may use the New York Heart Association (NYHA) functional class system to make this evaluation:

• Class I: Mild disease, ordinary physical activity may not be limited.
• Class II: Moderate disease, ordinary activity causes symptoms.
• Class III: Moderately severe disease, less-than-ordinary activity causes symptoms.
• Class IV: Severe disease, symptoms occur during rest, and any physical activity makes them worse.

However, this system is not foolproof, because even serious heart disorders may cause no symptoms if people reduce their activity level to compensate for the disorder.

Last full review/revision October 2012 by Lyall A. J. Higginson, MD