To evaluate the association of heart rate (HR) response with abnormal scan and/or left ventricular (LV) function in patients undergoing adenosine myocardial perfusion imaging, we retrospectively studied 188 consecutive patients who underwent a standard adenosine stress test (without exercise) and myocardial perfusion imaging (MPI) using technetium-99m sestamibi radioisotope. Change in HR was calculated by subtracting HR at rest from peak HR. The percentage change in HR was calculated. All patients underwent stress and resting single-photon emission computed tomography (SPECT) imaging. LV ejection fraction (EF) was calculated using gated SPECT. Mean age was 60 ± 12 years and 135 of the patients (72%) were women. We divided the patients into 2 groups: group 1 (142 patients, 75%) had normal scans and group 2 (46 patients, 25%) had abnormal scans; abnormal scans were defined as presence of either fixed defects, reversible defects, or both. Average HR increased by 29 beats/min in the normal scan group compared with 19 beats/min in the abnormal scan group (p = 0.0004). Forty-seven patients (25%) had reduced EF (<45%). This group had an average HR and percentage HR increase of 20 beats/min (29%) compared with an increase of 29 beats/min (44%) in patients with normal EF (p = 0.002 and p = 0.002, respectively). Thus, a diminished HR response had a significant association with both an abnormal scan and reduced EF on adenosine MPI.