A firm diagnosis requires that two major or one major and two minor criteria are satisfied, in addition to evidence of recent streptococcal infection.

Major Criteria

1. Carditis: All layers of cardiac tissue are affected (pericardium, epicardium, myocardium, endocardium) The patient may have a new or changing murmur, with mitral regurgitation being the most common followed by aortic insufficiency.
2. Polyarthritis: Migrating arthritis that typically affects the knees, ankles, elbows and wrists. The joints are very painful and symptoms are very responsive to anti-inflammatory medicines.
3. Chorea: Also known as Syndenham´s chorea, or "St. Vitus´ dance". There are abrupt, purposeless movements. This may be the only manifestation of ARF and is its presence is diagnostic. May also include emotional disturbances and inappropriate behavior.
4. Erythema marginatum: A non-pruritic rash that commonly affects the trunk and proximal extremities, but spares the face. The rash typically migrates from central areas to periphery, and has well-defined borders.
5. Subcutaneous nodules: Usually located over bones or tendons, these nodules are painless and firm.

Minor Criteria:

1. Fever
2. Arthralgia
3. Previous rheumatic fever or rheumatic heart disease
4. Acute phase reactants: Leukocytosis, elevated eritrosedimentation rate (ESR) and C-reactive protein (CRP)
5. Prolonged P-R interval on electrocardiogram (ECG)

Evidence of preceding streptococcal infection: Any one of the following is considered adequate evidence of infection:

• Increased antistreptolysin O or other streptococcal antibodies
• Positive throat culture for Group A beta-hemolytic streptococci
• Positive rapid direct Group A strep carbohydrate antigen test
• Recent scarlet fever.