Electrocardiographic (ECG) and echocardiographic examinations and 24-h ECG Holter monitoring were carried out in 100 patients (age < 65 years) with rheumatoid arthritis (RA) of stages II-IV according to Steinbrocker's criteria. One hundred patients with osteoarthrosis, spondyloarthrosis and painful shoulder matched for age, sex and body surface area constituted the control group. All patients with myocardial infarction, hypertension, rheumatic fever or a history of diabetes were excluded. Cardiac involvement, evaluated by echo-Doppler cardiography, 24-h ECG Holter monitoring and an ECG at rest, occurred in 52 (52%) patients with RA and in 23 (23%) control group patients (p < 0.0005). In the RA group ECG examination, 1 mm ST depression in at least two consecutive leads was observed more frequently, and occurred statistically more frequently for the highest stage of RA according to Steinbrocker's criteria, highest level of functional index and longer duration of disease. The 24-h Holter ECG monitoring did not show any differences in frequency of rhythm disorders between the RA group and the control group. However, silent myocardial ischaemia episodes appeared more often in the RA group. An ECG examination revealed more cases of valvular heart disease, especially mitral insufficiency, in RA patients than in the control group. A mitral valve prolapse was noted in 6% of patients and a pericardial effusion in 4% of patients. Patients with RA were noted to have a larger diastolic left ventricular diameter and aortic root diameter, and smaller ejection fraction, mean velocity of circumferential fibre shortening and fractional shortening. The results of the examinations show that RA is associated with cardiac involvement in a significant proportion of cases.