Determination of left ventricular size and shape.

• The importance of ventricular size and shape in determining cardiac function has been recognized for over 80 years; the concept is embodied in the Frank-Starling mechanism and in Laplace's law of the heart. However, over this same period, chamber pressure and cardiac output rather than ventricular dimensions have been measured to assess cardiac function, largely because cardiac catheterization procedures have made these hemodynamic measurements readily obtainable. Moreover, measurements of individual atrial and ventricular dimensions have been difficult to accomplish and have not been obtainable on a regular basis until relatively recently. During the past 15 years, an increasing number of investigators have begun to correlate the traditional hemodynamic measurements of cardiac performance with the parameters that measure the mechanical properties of the heart wall. Such studies have required strict attention to changes in chamber geometry and their correlation with simultaneously occurring pressure and flow events. Dimensional studies involving isolated papillary muscles or the intact heart have demonstrated the importance of initial fiber length and velocity of shortening in defining contractile state (1-3). Physical properties of the intact ventricular wall such as tension or stress, elasticity, viscosity, and compliance have been defined from pressure-volume relationships (4-8). Measurements of left ventricular volumes have allowed the determination of beat-by-beat stroke volume, the quantification of regurgitant flow in valvular heart disease, the calculation of ejection fraction, and the in vivo estimation of left ventricular mass (9-15). The methods presently being used to measure cardiac chamber dimensions and volume in animals or man have been summarized in several recent re-