This retrospective study evaluated 933 patients referred for diagnostic nuclear medicine perfusion testing at 2 outpatient cardiology centers over a 7-month period. None of the patients were able to perform treadmill stress testing, and all received dipyridamole as a pharmacological stress. The authors found that 44% of the patients had an adverse reaction to dipyridamole. A correlational analysis of patients who did and did not have adverse reactions indicated that patients who exhibited some form of adverse reaction to dipyridamole were 10% more likely to have an abnormal perfusion test. In addition, age-group comparisons between patients 70 years or older and those younger than 70 years demonstrated that the younger group had a statistically greater probability of having an adverse reaction to dipyridamole.