In the era of big data, the utilization and analysis of large amounts of clinical data are imperative. The standardized structured medical information exchange version 2 (SS-MIX2) is a standard data storage format used in Japan to share clinical data from various vendor-derived hospital information systems. This storage format is divided into 2 categories: standardized and extension storage. Although the standardized storage includes clinical data such as basic patient data, prescriptions, and laboratory results, all other data are stored in the extension storage, because their formats are not standardized. In 2015, the Japanese Circulation Society developed the standard export data format (SEAMAT) for electrocardiography (ECG), ultrasound cardiography (UCG), and catheterization (CATH) data for the SS-MIX2 extension storage. Using physical examination and catheter report systems in accordance with the SEAMAT, specific cardiological data such as ECG, UCG, and CATH can be transferred to the SS-MIX2 extension storage, resulting in efficient secondary use of these data for research purposes. SEAMAT can aid in the effective establishment of a nationwide clinical database, and reduce tedious manual data input by clinicians and clinical research coordinators. Moreover, a program that enables the conversion of comma-separated data from information systems into SEAMAT can provide a useful and economical tool for transferring huge clinical data to the SS-MIX2.