Patients with heart connective tissue dysplasia (HCTD) are known to be subject to infectious and inflammatory diseases due to peculiarities of their immune system. We studied 181 patients with HCTD depending on thyroid hormone levels and vegetative dysfunction. HCTD was shown to be associated with a significant decrease of IgM levels and increase of circulating immune complexes. The IgG level in patients with mitral valve prolapse (MVP), anomalous chord localization, and combination of MPV and tricuspid valve prolapse was significantly higher than in the absence of HCTD. Patients with and without HCTD showed the dependence of IgA levels on TSH concentration. In those with combined MPV the intensity of chemiluminescence was related to the T4 level. The dependence of IgM levels on he presence ofvegetative dysfunction was documented in patients with MVP.