In this article, we have reviewed the impact of the new technique of Doppler ultrasound upon the assessment of aortic stenosis, aortic regurgitation, and diastolic left ventricular function. It is a powerful new technique that greatly extends our ability to understand the pathophysiology of these conditions. However, its use must be tempered with an appreciation of the limitations of the new technique and knowledge of the circumstances in which it may yield erroneous results.