Objective To evaluate the clinical efficacy of transthoracic two dimensional echocardiography, cardioangiography (CAG), and MRI in the diagnosis of cor triatriatum. Methods Twelve cases of cor triatriatum were confirmed by operation. Imaging examination was performed in 12 cases by transthoracic two dimensional echocardiography, 6 cases by CAG, and 8 cases by MRI. Results The diagnostic accuracy of cor triatriatum was 7 out of 12 by UCG, 4 out of 6 by CAG, and 8 out of 8 by MRI, respectively. MRI provided excellent delineation of the intraatrial membrane and the size of the membrane orifice. Conclusion MRI was of great value in the diagnosis of cor triatriatum.