CYP19A1 and myocardial infarction: Three of the four randomised controlled trials and one observational study that directly compared aromatase inhibitors with tamoxifen showed increased risks of myocardial infarction in the aromatase inhibitor group, with relative risks ranging from 1.50 to 2.29.18, 30, 32, 38, 44 However, the effect was statistically significant only in the observational study and one randomised controlled trial.