5% to 7% dynamic internal compliance is a number that is widely used internationally to produce vascular replicates into which implantable cardiovascular products can be deployed for testing. Fifteen years ago, Dynatek presented research to the NHLBI and undertook a major review of all found publications involved with the compliance of natural vessels either in vivo or in vitro. Dynatek suggested an average number of 5% to 7% change in diameter per 100 mm Hg internal pressure at 72 BPM to reasonably represent those conditions found in vivo . Although somewhat still controversial, most laboratories internationally now use this target. Data generated in laboratories all over the world can now be compared to each other because of the utilization of this common compliance for the testing.