Quantitative measurements of left ventricular volume and ejection fraction are useful in the management of patients with heart disease. Several imaging methods exist, but are limited by cost, invasiveness, or exposure to radio-isotopes. Conventional echocardiography is a noninvasive method that allows estimation of left ventricular size and function; however, quantitative measurements of volume are not widely used due to lack of reproducibility and inaccurate measurements. Real-time three-dimensional echocardiography is a new technique that can be used to derive volume measurements from a single image acquisition. We hypothesize that real-time three-dimensional echocardiography is an accurate method for making left ventricular volume measurements. We therefore propose to measure left ventricular volumes using real-time three-dimensional echocardiography in human subjects and correlate these measurements with magnetic resonance imaging, a more accurate noninvasive method for obtaining these measurements.