1.3 Concept of Testing New Parameters: In the current study, several steps of model reduction will be tested. Each reduction is intended to allow non-invasive measurements to become increasingly simple and feasible at reduced echo quality. The comparison with the gold standard will then reveal the costs of model reductions in terms of precision and predictive power. Since direct pressure measurements are not feasible non-invasively, some simplifications of the pump model are mandatory. The most useful is to reduce the heart to a 1-dimensional, piston-like pump system moving only in apico-basal direction (longitudinal function). In such a model, not only contractions, but also flow directions are longitudinal. The 1-dimensional Euler equation can then be used to calculate instantaneous atrio-ventricular pressure gradients from Color Doppler M-Mode echocardiograms. Similarly, apico-basal displacement of the 'piston' can easily be measured by M-Mode echocardiograms of the mitral annulus (mitral annular plane systolic excursion, MAPSE). When combined, the suction effect of the ventricle relative to the left atrium can be assessed. A further simplification consists of replacing MAPSE by the widely used Doppler tissue imaging (DTI) -parameters of systolic (s') and early-diastolic (e') velocity. The reference method of this study will consist of invasively measured suction work, against which the new parameters will directly be compared.