been built. three of them with improved characteristics are being successfully used, as shown in this article. the two important creative stages in tissue heart valves (from 1964 to 1971) took place in a short space of seven years and that since 1971 when the concept of 'man-made pericardial valves' was created, no other significant invention has occurred in this field except the use of bovine pericardium in the construction of transcatheter valves for aortic valve replacement. the porcine valve was used successfully under several names, made by different laboratories, with various modifications and slight improvements without becoming essentially different from the original, native, pig's valve shape. however, the porcine valve, although far from perfect, was very useful in helping a large number of patients over many years. the bovine pericardial valve had been created in 1971 and over the following 4 decades, with various modifications and improvements made by different , it became, due to its superior overall qualities, the tissue valve of choice for the great majority of surgical groups around the world. the pericardial valve is not simply another valve, it is the embodiment of a concept of tissue valve construction. at present the bovine pericardium is being used, tomorrow perchance an even better material will be found. in this respect, ionescu made, in one of his early papers, a significant and rather prophetic statement: the physico-chemical and biological properties of the natural porcine aortic valve have been profoundly altered by various interventions in order to adapt it for therapeutic means. in this way, the porcine valve has lost all its primordial characteristics except its shape which remains unchanged and unchangeable. the pericardial valve, on the other hand, has been conceived as an entirely 'man-made' valve and therefore its shape and general characteristics can be altered through a multitude of interventions in order to optimise its function adhuc sub judice lis est: quintus horatius flaccus (68-8 bc) addenda contrary to what is mentioned in this article, a short publication, co-authored by a. carpentier, was found. it presents a small series of 61 patients who received isolated aortic valve replacement with carpentier-edwards pericardial valves. the authors state that at 6 years of follow-up 'there have been no cases of periprosthetic leak, no cardiac insufficiency and no thromboembolism' this short article does not contain any other 'significant' information. in a recent publication dr. denton a cooley, who used a very large number of ionescu-shiley pericardial xenografts, mentioned the following: i still have surviving patients with functioning bjork-shiley and ionescu-shiley valves, some of which were implanted 30 or more years ago. there are now more than 40 years since doctor ionescu introduced, for the first time, the glutaraldehyde treated bovine pericardium in clinical use in the form of a three cusp heart valve (the ionescu-shiley pericardial xenograft). it is of interest to know that now, 40 years later, the bovine pericardium is still used in three medical/surgical devices. 1. the second generation of pericardial xenografts as described in the above article are used in large numbers. 2. for the manufacture of "transcatheter aortic valve implantation" devices which are used in progressively larger numbers of selected patients, especially in europe. 3. for the manufacturing of cardiac ventricular chambers in an experimental artificial heart under testing in a french laboratory.