Slight limitation of physical activity. Comfortable at rest, but ordinary physical activity results in fa- tigue, or dyspnea. Marked limitation of physical activity. Comfortable at rest, but less than ordinary activity causes fatigue, or dyspnea. Unable to carry on any physical activity without symp- toms.
Symptoms are present even at rest.
If any phy- sical activity is undertaken, symptoms are increased. Reference Diseases of the Heart and Blood Vessels - Nomenclature and Criteria for Diagnosis , 6th edition, Boston, Little Brown and Company, 1964.