Doppler echocardiography is a diagnostic method that uses sound waves to provide images of heart structures and to assess blood flow. This imaging technique can been used to analyze peak aortic velocity, the speed at which blood is ejected from the left ventricle of the heart into the aorta (a major blood vessel carrying oxygenated blood to vessels throughout the body). Peak aortic velocity is used as a measure of left ventricular function. These measurements have been used to evaluate patients with heart attack, heart muscle disease associated with dilation of the heart, and congestive heart failure, as well as patients undergoing exercise testing. Studies have shown that loading conditions, specifically preload and after load, have effects on indicators of left ventricular function. Afterload is the stress that develops in the ventricle muscle wall during contraction (systole), whereas preload is the volume of the ventricle at the relaxation phase of the heart cycle (diastole). One study showed that methoxamine, an agent that increases afterload, but has no effect on preload, caused a decrease in aortic peak velocity. Another study showed that reduced afterload and elevated preload are associated with increases in aortic peak velocity. Both studies found that only slight changes in afterload or preload were associated with marked changes in aortic peak velocity. The results of previous studies are consistent with the effects of loading on aortic peak velocity. Impaired function of the left ventricle, the use of drugs that alter loading conditions, and age may interfere with the accurate interpretation of results from Doppler echocardiography. Thus, the effects of preload, afterload, heart rate, and age should be considered when evaluating ventricular function by Doppler echocardiography. (Consumer Summary produced by Reliance Medical Information, Inc.)