It is with great pleasure that we here present Artificial Heart 4 (proceedings of the 4th international symposium on artificial heart and assist devices). The symposium was held in Tokyo, Japan, on August 7 and 8, 1992 under the patronage of Mr. Hiromitsu Yoshioka, Chairman of the Board of Trustees, Tokyo Women's Medical College. Artificial heart 4 consists of the papers presented in nine sessions: Oral Presentations A to E, Forums 1 to 10, and nine lectures by invited guest speakers from the United States and Europe. In this volume, papers from two new sessions, sessions IV and VII, entitled New Approaches, were prepared for devices and systems developed according to new ideas. Twenty-one papers in these two sessions were presented in five Forums (3, 4, 7, 8, and 9). Session VI was provided to deal with heart transplantation, which is now closely related to both ventricular assist systems (VAS) and the total artificial heart (TAH). In this session, papers by two guest speakers from major heart transplantation centers in Europe were included.