Several geometric algorithms have been applied to estimate left ventricular wall volume (Vwall) from two-dimensional echocardiograms but have not been validated in eccentrically hypertrophied hearts. These algorithms can be fitted to the general formula: Vwall = k.Ao.Lo = k.Ai.Li, where Ao and Ai are the outer (epicardial) and inner (endocardial) short-axis areas, Lo and Li are the corresponding long-axis lengths, and k is a constant. The simplifying assumption that Lo and Li are equal yields Vwall = k.Awall.Lo, where Awall = Ao - Ai. In 20 unsedated dogs (10-30 kg), including 10 with aortic regurgitation of 1-18 wk duration, the relationship between actual Vwall (determined postmortem) and Awall.Lo was not significantly different from the line of identity (Vwall = 1.01 Awall.Lo + 0.5 ml, r = 0.98, SEE = 3.5 ml), indicating k was not significantly different from 1. There was no significant difference between predicted and actual Vwall over a range of 31-105 ml, and interobserver variability was 4.1%. The simple area-length product, Awall.Lo, accurately predicts Vwall of both normal and volume-overloaded hypertrophied canine left ventricles and is thus suitable for serial observations of hypertrophic adaptation to volume overload.