Molecular biology in cardiology, a paradigmatic shift.

Control of the performance of the heart can now be understood in terms of three paradigms: beat-to-beat, length-dependent regulation (Starling's Law of the Heart); short term regulation by biochemical changes within the cardiac cell (excitation-contraction coupling, myocardial contractility); and long term regulation by altered gene expression (molecular biology). The latter may also compensate for inhomogeneities in ventricular function. According to Kuhn's theory, the more recent of these paradigms should provide a better and more complete picture of cardiac function. However, because each of these paradigms explains distinct aspects of cardiac regulation that are not mutually exclusive, this evolution fails to support Kuhn's view that science progresses as a series of revolutionary advances. Instead, it is only by understanding all of these paradigms that we can begin to grasp their complex interactions in governing cardiac function, and so gain insight into these interwoven control mechanisms. It seems likely that this is not an uncommon pattern, and that future work will add new paradigms to the complex body of knowledge of cardiac regulation without invalidating any of the paradigms described in this editorial.