(123)I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy is one of only a few methods available for objective evaluation of cardiac sympathetic function at the clinical level. Disorders of cardiac sympathetic function play an important role in various heart diseases, and MIBG provides an abundance of useful information for the evaluation of severity, prognosis and therapeutic effects; this is particularly useful in cases of heart failure, ischaemic heart disease and arrhythmic disease. On the other hand, the quantitative indices for MIBG differ between institutions, and evidence has not been sufficiently well established for MIBG scintigraphy when compared with myocardial perfusion imaging in ischaemic heart diseases. In consideration of these difficulties, this review provides fundamental information regarding MIBG, its usefulness for various diseases and future difficulties.