123I-metaiodobenzylguanidine (MIBG), a tracer for sympathetic neuron integrity and function, was applied to 155 patients with various types of cardiac disease. The methods for quantification of MIBG and washout were studied as well as normal ranges. Heart-to-mediastinum average count ratio (H/M) correlated well with total heart count divided by injected activity (r = 0.60, P < 0.0001 and r = 0.72, P < 0.0001 for early and delayed images, respectively). Although as a whole left ventricular ejection fraction (LVEF) positively correlated with H/M ratio, decreased H/M ratio could be associated with normal LVEF, which may indicate that the MIBG activity was an independent variable compared with cardiac contractility. High washout rate was seen in various cardiac diseases, such as dilated cardiomyopathy, hypertrophic cardiomyopathy, ischaemic heart disease, hypertension, hypothyroidism and arrhythmia. The increased washout seems to be nonspecific to disease type, but is a common feature of damaged or failing myocardium.