The New York Heart Association (NYHA) Functional Classification[1] provides a simple way of classifying the extent of heart failure. It places patients in one of four categories based on how much they are limited during physical activity; the limitations/symptoms are in regards to normal breathing and varying degrees in shortness of breath and or angina pain.

It originated in 1928,[2] when no measurements of cardiac function were possible, to provide a common language for physicians to communicate. Despite difficulties in applying it, such the challenge of consistently classifying patients in class II or III,[3] because functional capacity is such a powerful determinant of outcome it remains arguably the most important prognostic marker in routine clinical use in heart failure today.

NYHA Class Symptoms
I Cardiac disease, but no symptoms and no limitation in ordinary physical activity, e.g. shortness of breath when walking, climbing stairs etc.
II Mild symptoms (mild shortness of breath and/or angina) and slight limitation during ordinary activity.
III Marked limitation in activity due to symptoms, even during less-than-ordinary activity, e.g. walking short distances (20–100 m).
Comfortable only at rest.
IV Severe limitations. Experiences symptoms even while at rest. Mostly bedbound patients.

Another frequently used functional classification of cardiovascular disease is the Canadian Cardiovascular Society grading of angina pectoris.