Gated magnetic resonance imaging of 5 patients with suspected constrictive pericardial disease was performed using a superconducting magnet operating at 0.35 Tesla. Results were compared with those of echocardiography and hemodynamic measurements in all patients, with chest films in 5, computerized tomography in 2 and with histologic findings in 3. Pericardial thickness exceeded 5 mm in 4 patients and was 5 mm in 1 patient. Absence of magnetic resonance signal from the thickened pericardium was observed with extensive calcific deposits, and increased intensity of the thickened pericardium was associated with inflammatory disease. Dilatation of the right atrium, venae cavae and hepatic veins, and right ventricular narrowing was observed in all patients. The ventricular septum was straight in all patients. Magnetic resonance imaging allows both measurement of pericardial thickness and depicts internal cardiac anatomy without exposure to radiation or use of contrast medium. Satisfactory imaging with a large field of view can be performed in the presence of lung disease, thoracic deformity or surgical "hardware"--conditions that limit echocardiography and computerized tomography. The inherently 3-dimensional data permit imaging in any plane without loss of resolution. Thus, magnetic resonance appears to be the noninvasive method of choice for the diagnosis of constrictive pericardial disease.