We developed a new ultrasonic triangulation technique to measure regional wall thickness and shear motion of the left ventricular wall under normal conditions and during complete and partial coronary occlusions. In 10 open-chest dogs, a left ventricular micromanometer was inserted, and a screw-driven arterial clamp and flowmeter were placed around the left circumflex coronary artery. A single miniature ultrasonic crystal was placed in the subendocardium of the left ventricular free wall in a region to be made ischemic, and three receiving crystals were sutured to the opposing epicardium at the corners of a 45-degree right triangle. By the trigonometric combination of three measured lengths from ultrasonic dimension gauges, the exact position of the endocardial crystal in X, Y, and Z coordinates could be displayed by computer. The endocardial surface moved in a longitudinal direction relative to the epicardial surface during normal systole [0.58 ± 0.26 (mean ± SEM) mm]. With coronary occlusion, this myocardial shear became less marked (0.11 ± 0.12 mm), and systolic wall thickening changed to thinning. When coronary occlusion was released, end-diastolic wall thickness and percnt wall thickening rapidly increased to 104.8% and 141.7% of control, respectively, concurrent with the reactive hyperemia. With partial coronary constriction, these postreperfusion changes were markedly reduced, suggesting a role for reactive hyperemia in postreperfusion wall thickness dynamics. These techniques allow measurement of shear and three-dimensional display of dimensions and thereby permit documentation of true wall thickness dynamics both during and after coronary occlusion.Circ Res 47:173-181, 1980