Left ventricular mass (LVM) is an important consideration in the management of cardiac hypertrophy associated with hypertrophic cardiomyopathy (HCM), systemic hypertension, and other diseases. A brief MRI cardiac imaging procedure used to monitor regression of LVM during treatment would be beneficial in management of these patients, since echocardiograms cannot be obtained in all patients and since the volume of a hypertrophic heart can straightforwardly be assessed from a series of tomographic slices. The present study was designed to evaluate a brief cardiac MRI procedure for measurement of LVM in HCM and compare it to echocardiography. MRI images acquired in a simulated transverse body plane were used to evaluate the mass of the left ventricle in 6 ex vivo human hearts obtained at autopsy. The estimates of LVM by MRI in the ex-vivo hearts were within 8% of the actual LVM. MRI images were acquired to evaluate LVM in 5 normal subjects and 12 patients diagnosed with HCM. Echocardiography was accomplished on 4 of the normal subjects and 10 of the patients having HCM. There were no significant differences in LVM by MRI and echocardiographic techniques in normal subjects. Transverse MRI images acquired on normal subjects demonstrated that estimates of LVM are reproducible when repeated over 3-w to 3-mo intervals. Images selected for analysis represented the heart in an early diastolic phase. MRI and echocardiographic techniques demonstrated significant differences in LVM in HCM patients. Estimates of LVM in normal subjects and patients diagnosed with HCM were normalized for body weight. The LVM estimates for HCM patients were very significantly different than normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)