Left ventricular (LV) dimensions and shortening at rest and during treadmill exercise were examined before and after 4 weeks of pulmonary artery (PA) constriction in 6 conscious dogs. The dogs were preinstrumented with LV and right ventricular (RV) catheters, an LV micromanometer, a PA inflatable cuff occluder and ultrasonic crystals to measure an LV anteroposterior, a septal-lateral, an apex-base and a free wall segment chord. With PA constriction, RV pressures increased from 49 +/- 4/2 +/- 1 mm Hg (systolic/end-diastolic) to 104 +/- 5/2 +/- 1 at rest and from 71 +/- 9/2 +/- 1 to 133 +/- 8/14 +/- 2 at peak exercise (mean +/- standard error of the mean). Heart rate, LV pressure and LV dP/dt were similar before and after RV pressure overload at rest and with exercise. During exercise at control, systolic shortening increased significantly in all chords. With chronic PA constriction at rest, shortening of all chords also remained normal despite decreases in end-diastolic dimensions, which were most marked in the septal-lateral chord (23% decrease, p less than 0.01). However, during exercise in the presence of RV pressure overload, septal-lateral shortening decreased 46% (p less than 0.01) despite increases in systolic shortening in the other chords similar to the control response. Therefore, although LV function at rest in chronic RV pressure overload is normal, exercise may induce regional abnormalities of LV contraction that appear to be mediated by a reduced contribution of the ventricular septum to LV ejection.