A retrospective review of 47 patients with progressive systemic sclerosis revealed a highly significant (P less than 0.001) association between myositis and myocarditis. Three patients developed clinically overt myocarditis as an early feature of their disease. These patients had an inflammatory myopathy indistinguishable from polymyositis. Despite an excellent clinical response to steroids, the late occurrence of life-threatening conduction system defects appeared while they were receiving therapy. Consequently, patients with progressive systemic sclerosis and myositis should be evaluated for a coexisting myocarditis. The findings in these patients lend further support to the concept of a generalized myopathic process among the connective tissue diseases.