The ability of magnetic resonance imaging to evaluate right ventricular architecture and size was assessed in 149 subjects (26 normal volunteers and 123 patients with heart disease). The right ventricular myocardium was clearly delineated from adjacent structures in all patients. The trabeculated pattern of the right ventricle was well seen and was most evident during systole and in patients with right ventricular hypertrophy. The moderator band was discernible in 72% of the subjects, whereas smaller muscular structures such as the papillary muscles were identified less frequently. Magnetic resonance imaging provided a good image of the tricuspid valve leaflets but did not show the pulmonic leaflets well. The clear visualization of the endocardial and epicardial borders obtained with magnetic resonance imaging allowed measurement of wall thickness and of the internal dimensions of the cavity in normal subjects, in patients with moderate to severe systolic overload, and in patients with moderate to severe diastolic overload. Patients with severe systolic overload of the right ventricle had markedly thicker walls when compared with patients without this condition. The mean internal dimension at end diastole of patients with severe diastolic overload of the right ventricle was significantly increased when compared to other subgroups. Magnetic resonance imaging provides tomographic images of the right ventricle with clear distinction of the endocardial and epicardial surfaces that can be useful for quantitative and qualitative assessment of this complex structure.