[Coronaro-myocardial interplay determining the instantaneous mean ventricular shape (author's transl)].

A working hypothesis on the mechanism of diastolic chamber expansion based on functional anatomy and physiology is developed. It should be a major determinant of the momentary average chamber width. The sum of all intramyocardial fluid-filled spaces and the myocardium itself are considered in the working hypothesis as the hydraulic medium of a process which can be summarised under the term "cavernous body mechanism". The most important factor of this hydraulic system should represent the intramural fluid volume (hydraulic medium) and the contractile-elastic tension development in the transmural direction of the chamber wall. Morphological analysis of myocardial structure shows that an endoepicardial direction of force in the myocardial net can be recognised. The "motor" of circular fibres of the middle layer is surrounded by the spiral course of the fibres of the inner and outer layers of the chamber wall (uvula mechanism). It is interwoven by very dense bifurcating myocardial fibres (structural principle of the tongue). By these means, the width of the chamber cone is influenced decisively by an active decrease in wall thickness. The coronary perfusion pressure is thought to have a chamber dilating influence in the sense of a "cavernous body mechanism". The hypothesis presented helps us to understand pathological chamber dilation secondary to transmural myocardial fibrosis. Such a narrow functional coronary-myocardial interaction gives the myocardium two functions; besides haemodynamic pumping, the cardial muscle must function as an internal antagonist to favour diastolic chamber dilation.