A study to examine mid- and long-term outcomes in patients with subclinical carditis was conducted. Data obtained at the time of diagnosis and during the follow-up of 158 patients diagnosed with subclinical carditis were retrieved and analyzed. Most patients had isolated mitral insufficiency. Frequency of morphological changes in the mitral valve was significantly lower in patients with at least one additional Jones criterion both at baseline (10.3% vs. 48.8%, p < 0.01) and at the end of the follow-up (27.8% versus 43.5%, p = 0.11). Mean jet size for mitral (12.0 +/- 8.8 versus 18.2 +/- 5.5 mm, p < 0.01) and aortic (4.1 +/- 4.0 versus 14.0 +/- 5.8 mm, p = 0.008) insufficiency were decreased compared to baseline. Improvement in mitral insufficiency was more frequent among patients with more than five years of follow-up (82.6% versus 60.0%, p = 0.039). Subclinical carditis due to acute rheumatic fever is not a benign and temporary condition. These patients should be given secondary prophylaxis.