M-mode and two-dimensional echocardiography have greatly enhanced the evaluation of animals with congenital cardiac disease. Structural abnormalities can be seen and hemodynamic alterations inferred, e.g., ventricular wall concentric hypertrophy indicating pressure overload to the respective ventricle. Interrogation of the diseased heart by Doppler echocardiography allows acquisition of more direct hemodynamic information without cardiac catheterization, which enables the clinician to give a more precise description of a congenital abnormality. The purpose of this study is to illustrate and describe abnormal blood-flow patterns in selected congenital cardiac defects in animals. Basic background information concerning Doppler echocardiographic principles, flow patterns, and calculations will be briefly discussed. For more detailed descriptions other references should be sought. Interpretation of Doppler echocardiography in animals is based primarily on data derived from human studies since studies involving measurable numbers of veterinary patients have not yet been completed.