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...