Although cardiac abnormalities have been reported in patients with idiopathic polymyositis-dermatomyositis (PM), the nature and extent of these abnormalities have varied. The purpose of this study was to determine the prevalence and to obtain a better description of the spectrum of cardiac abnormalities in a cohort of patients with PM by use of a thorough noninvasive cardiac evaluation. Accordingly, we studied 26 patients with a history of PM and clinically inactive myositis (22 polymyositis, 4 dermatomyositis) between June 1984 and June 1991. Examination included history, physical examination, 12-lead electrocardiography, 24-h ambulatory electrocardiographic monitoring, chest radiography, transthoracic echocardiography, and radionuclide ventriculography. Of the patients studied, 77% were taking corticosteroid medications at a mean dose of 39 +/- 27 mg at the time of their evaluation. All 26 patients were identified as having two or more cardiac abnormalities. Cardiac symptoms and signs were common (62 and 81%, respectively), but were generally nonspecific. Electrocardiographic findings were most common (in 85% of cases), followed by findings on ambulatory monitoring (77%), echocardiography (42%), and radionuclide ventriculography (15%). The prevalence of mitral valve prolapse (8%) and hyperkinetic left ventricular contraction (12%) was significantly lower than previously reported. A secondary aim of this study was to determine associations between demographic variables including age, disease duration, cardiovascular symptoms, immunosuppressive therapy, autoantibody status, and creatinine phosphokinase level, and the presence of cardiac abnormalities. Of these patient variables, only increasing patient age was associated with an increased likelihood of cardiac abnormalities on noninvasive testing.(ABSTRACT TRUNCATED AT 250 WORDS)