This paper was originally commissioned by the UK Department of Health as a contribution to the work of its Biomaterials and Implants Research Advisory Group. This group was set up under the Chairmanship of Professor Sir Colin Berry with the following terms of reference: (i) to identify recent advances in the field of biomaterials; (ii) to consider the future contribution of biomaterials in improving human health; (Hi) to advise the Standing Group on Health Technology in areas where developments and assessment are needed; and (iv) to report to the Director of Research and Development (Professor Sir Michael Peckham) by October 1995. The cardiovascular field was one of several areas in biomaterials/implants considered by the Advisory Group. Amongst other areas considered were orthopaedics, dentistry, urology, wound repair and ophthalmology. Additionally, consideration was also given to such topics as chemical and biochemical sensors, drug release, hydrogels, membranes and artificial organs. The final report of the Advisory Group will be published at the end of this year. However, the Department has agreed that individual working papers such as the present one can be published independently in appropriate scientific journals.