Right Ventricular Contraction

Cyclic changes in the dimensions of the right ventricular wall were recorded continuously in 17 intact, unanesthetized dogs. The free wall of the right ventricle contracts synchronously. At six different locations on its surface, the average relative shortening was about 15%. At the onset of ventricular systole, the right ventricular wall expands while the intraventricular pressure abruptly rises. This initial systolic expansion of the wall represents a change in shape of the chamber without a change in volume since the valves are all closed at this instant. It may result from early contraction of papillary muscles, drawing the tricuspid valves down into the ventricular chamber, supplemented by the bulging of the interventricular septum which accompanies sphericalization of the left ventricle at the onset of systole. During feeding, the heart rate accelerates, and the systolic and diastolic dimensions are promptly reduced. During exertion, the heart rate increased, systolic ejection was much more complete and diastolic filling was somewhat reduced.