Some patients exhibit blunted hemodynamic response (BHR) to adenosine infusion during stress myocardial perfusion imaging (MPI). Objective: To investigate if patients with BHR are less likely to demonstrate abnormal MPI compared to patients with normal hemodynamic response (NHR). Methods: The frequency of abnormal MPI in 47 consecutive patients with BHR between March 2003 to May 2004 were compared with a 100 consecutive patients with NHR. The definition of BHR is an increase in heart rate < 10 BPM and a decrease of systolic blood pressure < 10 mmHg. Patients with arrhythmias were excluded. All patients underwent Thallium-201 rest SPECT followed by Tc-99m tetrofosmin gated stress SPECT. The characteristics of the abnormal MPI with regards to the presence of ischemia, scar or mixed scar and ischemia as well as scar size were obtained. Additionally, functional information in both groups was recorded. The results were statistically tested for significant differences. Results: The number of males, females and their mean age was 34, 13 and 70 yrs. in the BHR group and 49, 51 and 65 yrs. in the NHR group. There were 15/47 (32%) abnormal MPI in the BHR group versus 22/100(22%) in the NHR group (p=0.2). The 15 abnormal MPI in the BHR group demonstrated ischemia in 2 patients (4.3%), scar in 11(23.4%) and mixed scar and ischemia in 2(4.3%) while the abnormal 22 MPI in the NHR group demonstrated ischemia in 10(10%), scar in 4(4%) and mixed scar and ischemia in 8(8%). The mean left ventricular ejection fraction (LVEF) and end diastolic volume were 55.3+15.9% and 113.1+61.7ml in the BHR group and 60.4+12.0% and 95.6+35.3ml in the NHR group. The statistically significant differences between the two groups were in the number of studies demonstrating scar only (23.4% for BHR versus 4% for NHR, p=0.0007). Patients with BHR also tended to exhibit larger mean scar size (19.9+17.5%) compared to the patients with NHR (11.7+7.4%) (p=0.002). Conclusion: There is no significant difference in the frequency of abnormal MPI in patients with BHR compared to patients with NHR. However, patients with BHR more frequently have scars compared to patients with NHR. Also the scars tend to be significantly larger in patients with BHR.