Myocardial fibrosis is found at postmortem examination in up to 80% of patient with scleroderma, yet many such patients have an entirely normal cardiovascular examination. Isometric handgrip exercise is a useful abnormality. By this method 15 patients with scleroderma (American Heart Association criteria) were compared with 15 sex and age-matched normals. Results showed that scleroderma patients had a depressed heart rate response to handgrip (p less than 0.05) and abnormal systolic and diastolic time intervals. They showed a decreased shortening of the ratio pre-ejection period to ejection time (p less than 0.05) and a lengthening of the isovolumic relaxation time compared with the control group who steadily shortened this period (p less than 0.01). These findings indicate increased stiffness and impaired contractility of the left ventricle as would be caused by an underlying fibrotic process otherwise undetectable. Immunohistological studies give support to this concept. Staining with monospecific antibodies to collagens types I to V of cardiac muscle from patients who, in life, had no overt cardiac disease, showed an excess deposition of collagens type I, III, and IV. In conclusion isometric exercise may provide a noninvasive method of unmasking subclinical fibrosis of the left ventricle in scleroderma, and immunopathological studies support these findings.