What IS MY functional class?

Functional class is one way doctors assess the severity of your PAH symptoms.

The World Health Organization (WHO) created a system of 4 “functional classes” (FC) for patients with PAH. Class I means fewer symptoms and less restriction of activity. Class I symptoms are considered the least severe, and Class IV symptoms the most severe. Here are some basic criteria for each FC:

Class I

No symptoms with ordinary physical activity.

PAH functional class 1


Class II

Symptoms with ordinary activity. Slight limitation of activity.

PAH functional class 2

Walking 2 flights of stairs

Class III

Symptoms with less than ordinary activity. Marked limitation of activity.

PAH functional class 3

Walking 1 flight of stairs

Class IV

Symptoms with any activity or even at rest.

PAH functional class 4


Your functional class may improve with treatment, but there are multiple ways your doctor will monitor your PAH.