This presentation reviews and illustrates the published work relating to the diagnostic applications of cardiac ultrasound. It includes, in addition, the following previously unpublished observations from our laboratory. Patients with prolapsing mitral leaflets may show a systolic anterior movement of the anterior cusp of the mitral valve when recordings are made near the base of the leaflet. This is in contrast to the usual posterior steplike movement which is regularly recorded from the distal position of the cusp. In severe aortic valve regurgitation, the anterior mitral leaflet may show marked restriction of the opening movement and a very slow slope in diastole. These findings may be reversed by aortic valve replacement. Congestive cardiomyopathies show a typical dilatation of the left ventricular outflow tract and mitral valve with shallow opening movements but rapid diastolic slopes. Rapid fluttering of the aortic valve has been seen in patients with mitral regurgitation, ventricular septal defect, and myocardial dysfunction following coronary occlusion. These fluttering movements are thought to represent abnormal left ventricular ejection. Aortic valve disease may be simulated by calcific deposits in the aortic wall or adjacent structures. The abnormal echo complex disappears when the transducer is angled slightly medially and is replaced with normal valvular motion patterns. Left atrial myxomas, present as typical abnormal echo patterns within the cavity of the left atrium, should be sought here as well as behind the mitral leaflet. Their removal is accompanied by a loss of abnormal echo patterns and a decrease in the size of the left atrial cavity. Pulmonic regurgitation may be identified, on occasion, by a rapid diastolic fluttering of the tricuspid valve identical to that seen in the mitral valve in the presence of aortic regurgitation. The tricuspid valve may exhibit markedly diminished diastolic slopes in the range ordinarily associated with tricuspid stenosis, in patients without evidence of this condition. This is believed to result from restrictive processes involving the right heart. The recognition of pericardial fluid in the transverse sinus of the pericardium, in front of the aortic root, and on the diaphragmatic surface of the heart is expected to enhance the diagnostic accuracy of echocardiography in this condition. The outflow tract of the left ventricle can be demonstrated by "scanning" the transducer from the aortic root to the mitral valve. The typical abnormal configuration seen in tetralogy of Fallot consists of a widened aortic root which straddles the interventricular septum.