ECG-gated magnetic resonance imaging (MRI) was performed for healthy volunteers and for patients with various heart diseases, and its usefulness was compared with that of two-dimensional echocardiography. For this study, several modifications were made in the MRI equipment used. First, a surface coil was introduced for recording the MR signal, resulting in a high S/N ratio. Second, an oblique scan mode was developed for selecting freely the slices similar to those chosen by two-dimensional echocardiography. For imaging, the back projection method and spin echo (SE) pulse sequence were chosen to minimize motion artifacts caused by cardiac beats. In this study, left ventricular wall thickness and left ventricular volume were estimated from gated MR images, taken both in the horizontal and oblique longitudinal scan modes. The results were as follows: The anterior, inferior and apical left ventricular walls were clearly visualized with oblique longitudinal scan images. The thickness of the interventricular septum and posterior wall were measured on left ventricular horizontal scan images. Each measurement was compared with data obtained by two-dimensional echocardiography. Both correlation factors were about 0.70, indicating poor correlations. Left ventricular ejection fraction was calculated from left ventricular volume estimates. Comparison of left ventricular ejection fractions estimated by MRI and two-dimensional echocardiography revealed a close similarity. We concluded that MRI is useful for non-invasive evaluation of cardiac function, and in detecting wall thickness abnormalities due to various heart diseases.