This study aimed to evaluate the effect of adenosine on epicardial coronary artery diameter during ergonovine provocation testing. A total of 158 patients who underwent an ergonovine provocation test with intracoronary adenosine injection between 2011 and 2014 were selected. Patients were divided into four groups based on the severity of percent diameter stenosis following intracoronary ergonovine administration: Group 1, induced spasm < 50%; Group 2, 50-89%; Group 3, 90-99%; and Group 4, total occlusion. Spasm positivity was observed in 44 (27.8%) cases in the study population (mean age, 57.4 ± ± 10.7 years). Intracoronary adenosine increased the diameter of the ergonovine-induced epicardial artery by 0.51 ± 0.31 mm, 0.73 ± 0.39 mm, 0.44 ± 0.59 mm, and 0.01 ± 0.04 mm in Groups 1, 2, 3, and 4, respectively. Subsequent administration of nitroglycerin further increased vessel diameter by 0.49 ± 0.28 mm, 0.93 ± 0.68 mm, 2.11 ± 1.25 mm, and 2.23 ± 0.69 mm in Groups 1, 2, 3, and 4, respectively. The ratios of adenosine-induced diameter to reference diameter were significantly lower in patients with spasm positive results (0.68 [0.59-0.76] vs. 0.18 [0.00-0.41], p < 0.001 in the study population; 0.60 [0.54-0.67] vs. 0.40 [0.27-0.44], p < 0.001 in Group 2) with the best cut-off value of 0.505 (sensitivity 0.955, specificity 0.921). Intracoronary administration of adenosine dilated the ergonovine-induced vasoconstricted epicardial coronary artery. The ratio of adenosine-induced diameter to reference diameter was significantly lower in patients with spasm positive results.