Performance characteristics of the left ventricle during and following induced extrasystoles

During the last two decades, since the heart has become a direct target for various surgical procedures for the correction of several abnormalities, interest in understanding its basic regulatory mechanisms and performance has increased considerably. Many experiments have been devised to study cardiac performance, under different circumstances, as an isolated preparation or as an integrated part of a functioning system. The results derived from these investigations not only proved to be important conceptual tools in making many observed phenomena more readily comprehensible, but also provided us with valuable basic principles to treat cardiac patients before and after open heart operations. The purpose of this paper is to investigate the control of the function of the heart in dogs with the chest and pericardium open, and under strictly controlled conditions. In spite of all the work j done in this field, there still exists some degree of confusion regarding the relative importance of autoregulatory mechanisms and extrinsic factors governing cardiac performance. Without trying to take sides as to the priority of either of these mechanisms, we have made an effort to confine our interest mainly to the intrinsic autoregulation of the heart