Magnetic resonance imaging is a newly developed diagnostic technique recently used for the study of the cardiovascular system. One of the most promising fields of application for magnetic resonance is the study of congenital heart diseases. Since it offers high contrast and resolution tomographic images of the heart, this technique appears particularly suitable for the anatomic assessment of cardiovascular malformations. In order to evaluate the potential of magnetic resonance imaging in the evaluation of congenital heart diseases, we reviewed 21 cases of cardiac malformations (age: 9-81, mean: 48 +/- 23). Two dimensional echo-cardiography was performed on all of them. Out of the 21 patients, 13 were imaged to confirm previous diagnoses based on echocardiographic (8) or angiographic (5) data. Four more patients underwent a cardiac angiography after the magnetic resonance study. The remaining eight patients were imaged due to a poor echocardiographic examination (4) and for other reasons (4). Eight patients had an atrial septal defect, 1 had a patent foramen ovale, 2 had a ventricular septal defect, 1 had a corrected transposition of the great vessels, 2 had an aortic coarctation, 2 had a developmental venous abnormality, 5 had different congenital diseases of the aorta or of the pulmonary valve or artery. Image quality was optimal in 18 out of the 21 patients studied (85.7%). In the remaining 3 subjects image quality enabled a diagnosis. In all patients magnetic resonance imaging correctly depicted the cardiac malformation and in some cases furnished data on the severity of the disease. In 9 cases (4 atrial septal defects, 2 developmental venous abnormalities, 2 aortic aneurysms, 1 right pulmonary artery atresia) magnetic resonance imaging provided the diagnosis. These data indicate that magnetic resonance imaging may represent an important non-invasive diagnostic tool capable of offering valuable information on adult patients with suspected congenital heart disease. It is also possible to foresee that this technique will play an outstanding role as a non invasive alternative imaging technique whenever echocardiography cannot be performed is not satisfactory. Furthermore, magnetic resonance imaging should be considered a major diagnostic technique to be used for the anatomic study of the heart prior to resorting to angiography.