Echocardiography is a noninvasive diagnostic tool which has the capacity to provide reliable information on cardiac anatomy and function without risk or discomfort to the patient. The quality and quantity of information obtained in any given study is highly dependent upon the skill of the examiner. The anatomic and physiologic data obtained through its use in the severely ill infant allows immediate separation of infants with serious anatomic cardiovascular defects from those with conditions simulating heart disease. In some cardiac defects the echographic findings are specific enough to allow an accurate diagnosis.