We quantitatively compared the extrasystolic and postextrasystolic responses of the right ventricle and left ventricle of the same heart, which have vastly different geometries, architectures, and muscle masses. We studied nine isolated, supported canine hearts whose right and left ventricles were made to contract isovolumically with balloons placed in both chambers. The ventricles were paced with the following pattern: 20 regularly timed priming stimulations, followed by a test stimulation at a variable test pulse interval, and, finally, by a second test stimulation which was always delivered 1200 msec after the first test pulse. In each heart, approximately 15 different test pulse intervals between 300 and 1200 msec were investigated. Both the maximum developed pressure and maximum rate of pressure development, expressed as a percentage of their steady state values during the priming period were used to quantify the extra- and postextrasystolic responses. For each extrasystolic and postextrasystolic test beat, the normalized response of the right ventricle was plotted vs. that of the left ventricle. The regression line and correlation coefficient between the two were determined. The average result from nine hearts gave a slope of 0.96 +/- 0.05, an intercept of 4.52 +/- 4.05% and a correlation coefficient of 0.995 +/- 0.004. This analysis indicated that, despite the differences in right and left ventricular geometry, architecture, and mass, their force-interval behaviors were nearly identical.