High-resolution real-time 3-dimensional echocardiography (RT3DE) allows observation of the left ventricular endocardial surface in vivo. This study was performed to characterize the endocardial surface structure and its contractile function in the myocardial infarction (MI) zone in relation to the healing stage. RT3DE was performed in 90 subjects: 10 normal subjects, 50 patients with Q-wave MI 2 weeks after onset (acute MI), and 30 patients >2 months after onset (healed MI). Recordings of the left ventricular endocardial surface allowed observation of the endocardial structure in 76 patients (84%) from the apical window. The endocardial surface of normal myocardium has rough muscle folds that shrink during systole, implying endocardial contraction. In acute MI, the endocardial surface had lost systolic contraction, but appeared as normal surface structure and showed normal acoustic intensity. The endocardial surface of healed MI showed loss of systolic contraction, disappearance of folds (smooth surface), and high acoustic intensity. The frequencies of smooth surface and highest acoustic intensity were significantly higher in healed MI than acute MI (72% vs 32%, 68% vs 37%, p <0.05, respectively). Loss of systolic endocardial contraction was a common finding of Q-wave MI irrespective of the healing stage, and we could roughly estimate the size of the MI from the spatial extent of the noncontractile zone with reasonable reproducibility (r = 0.90, p <0.001). In conclusion, RT3DE is a new modality that allows observation of the structure and contraction of the endocardial surface of the left ventricular wall. We can make rough estimation of the size of the MI and its healing stage from endocardial observation with RT3DE.