Objective . We developed and evaluated a new method to automatically measure regional left ventricular wall thickening by analyzing the radiofrequency backscatter signal from an intracardiac echocardiographic catheter. Methods . We inserted 10-MHz echocardiographic catheters in 11 dogs. Wall thickness was perturbed by altering loading conditions and inotropic state. The backscatter signal from a single selected radial scan line was digitized. An automated algorithm identified the digitized endocardial and epicardial signals, tracked them throughout the cardiac cycle, and plotted the spatial difference over time. Pressure-thickness loops were generated. Results . End-systolic and end-diastolic thickness and percent wall thickening from the unedited, unsmoothed signals compared favorably with independent manual analysis of transthoracic echocardiographic images of the same region: r = 0.89 for wall thickness and 0.81 for systolic thickening. Conclusion . The backscatter signal from an intracardiac echocardiographic device can be analyzed automatically to continuously assess regional left ventricular wall thickening and generate pressure-thickness loops. (J Am Soc Echocardiogr 1998;11:1020-6.)