We determined whether tumor necrosis factor-alpha-converting enzyme (TACE) is expressed with tumor necrosis factor-alpha (TNF-alpha) in myocarditis.Tumor necrosis factor-alpha-converting enzyme, which has recently been identified as belonging to the family of metalloproteinase disintegrin proteins, is responsible for the conversion of TNF-alpha precursor to its mature form.We examined TACE and TNF-alpha expressions in endomyocardial biopsy tissues obtained from 14 patients with myocarditis and five control subjects by using quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry.Expression of TNF-alpha and TACE messenger ribonucleic acid (mRNA) was significantly greater in the myocarditis group than in the control group. A positive correlation was found between TNF-alpha and TACE mRNAs (r = 0.83, p < 0.05). Six patients with severe myocarditis underwent repeat biopsies. Although TNF-alpha and TACE mRNAs were expressed at high levels in the initial biopsies, a marked decrease was noted in the repeat biopsies. The immunostainings for TNF-alpha and TACE were positive in the myocytes and interstitial cells of myocardium obtained from patients with myocarditis. Expression of TACE and TNF-alpha mRNAs was greater in the subgroup in New York Heart Association functional class III or IV than in the subgroup in class I or II. Expression of TACE and TNF-alpha mRNA was correlated positively with left ventricular volume (TNF-alpha: r = 0.85; TACE: r = 0.80) and negatively with left ventricular systolic function (TNF-alpha: r = -0.85; TACE: r = -0.85).These findings indicate that the expression of TNF-alpha and TACE may have important implications in the pathogenesis of myocarditis and may influence advanced cardiac dysfunction in myocarditis.