For over 30 years, animal models have remained a central critical component in the pre-clinical safety evaluation of prosthetic heart valves developed for use in humans. Though many advances have been made in valve design, no ideal replacement prosthesis has yet been developed. As a result, valve manufacturers continue to address issues relating to thrombogenicity, structural integrity, fluid dynamics and calcification in their designs. Many animal models have been developed to examine these issues, including dog, pig, calf and sheep, yet no standard model has been accepted. Recently, the International Standard Organization has provided guidelines in document 5840 to address cardiovascular implants. The aim of this report is to provide a summary of the current state of pre-clinical valve evaluation in animals. Changes in ISO 5840 will be addressed that have occurred between 1998 and the present date, and the role of current available animal models. The aim also is to provide rational guidance in the selection of appropriate animal models to match the purpose of valve implantation studies.