The relationship between baroreceptor sensitivity (BRS) and cardiac sympathetic nerve function after acute myocardial infarction (AMI) was investigated in 34 patients. BRS was measured during the Valsalva maneuver and cardiac sympathetic function was assessed by the washout rate (WR) of I-123 meta-iodo-benzyl guanidine (123I-MIBG) with planar image (global WR) and polar map analysis (regional WR). Gated left ventricular ejection fraction (LVEF) measured by left ventriculography as a parameter of ventricular function was measured with quantitative gated SPECT (QGS). The gated LVEF correlated with global WR (r=-0.36, p=0.034) and regional WR of normal area (r=-0.46, p=0.006), but not with BRS, although BRS correlated with global WR (r=-0.43, p=0.015) and regional WR of normal area (r=-0.72, p<0.0001). After AMI, baroreceptor function is linked to sympathetic activation, as elucidated by the regional WR of normal area, which suggests that separation of the infarcted area from the non-infarcted myocardium is necessary for evaluating sympathetic activation after AMI and that the regional kinetics of 123I-MIBG in the normal area are a more suitable marker of activated cardiac nerve function than global 123I-MIBG kinetics.