There are various kinds of diagnostic examinations in the field of clinical cardiology. In this field, information concerning cardiac structure, dimensions (hypertrophy and dilatation) and cardiac functions are inevitably important. Noninvasive methods are desirable. Except for radiological examinations, electrocardiography and ultrasonic echocardiography are 2 main examinations in cardiology. Holter monitoring is one of the recent topics in clinical electro-cardiology. It is useful for the detection of rest angina or variant angina. Recently "silent myocardial ischemia" has been studied by using this method. This method is also useful for the study of arrhythmia, which is a major cause of sudden death. Quantitative analysis of arrhythmia in the studies of antiarrhythmic drugs can also be done by Holter monitoring. Late potential is also a topic in electro-cardiology. Ultrasonic echocardiography can detect the changes of cardiac structure and function. Doppler echocardiography, developed recently, has made it possible to estimate intracardiac pressure (especially pulmonary arterial pressure) noninvasively. With esophageal echocardiography findings in left atrium, such as thrombus or myxoma in left atrium can be obtained. The most appropriate tool must be selected from the many kinds of diagnostic examinations for efficient clinical diagnosis and therapy.