The aim of this study was to clarify the relationship between cardiac sympathetic nervous activity (SNA) assessed by radioiodinated metaiodobenzylguanidine (123I-MIBG), an analogue of norepinephrine and cardiovascular functions in patients with chronic heart failure (CHF). Subjects were 17 patients with CHF. A dose of 111 MBq of 123I-MIBG was administered intravenously, and 5-minute anterior planar images were obtained 15 minutes (early image) and 3 hours (delayed image) after the injection. The heart/mediastinum (H/M) count ratio was defined to quantify cardiac 123I-MIBG uptake. The washout ratio (WR) of 123I-MIBG from the heart was calculated as follows: (early counts-delayed counts)/early counts x 100 (%). Echocardiography was performed on all patients within 1 week of 123I-MIBG scintigraphy to measure stroke volume index (SVI). Blood pressure and heart rate (HR) in the resting state were also recorded to calculate cardiovascular functions including cardiac output, pulse pressure (PP), and mean blood pressure. Significant linear correlations were found between the early H/M ratio of 123I-MIBG and SVI, and between the delayed H/M ratio of 123I-MIBG and SVI, respectively. WR of 123I-MIBG was correlated with HR, and was inversely correlated with SVI and with PP, respectively. It is likely that a decrease in SVI is associated with enhanced cardiac SNA in severe CHF. 123I-MIBG scintigraphy is effective in assessing the cardiac functional status and SNA in patients with CHF in vivo. Moreover, changes in PP and HR indicate well alteration in SNA.