PTGS1 and myocardial infarction: Interestingly, no significant differences in the occurrence of MI were detected between patients (n = 123) on aspirin prophylaxis [100 mg/day; inhibitor of cyclooxygenase 1 (COX-1)] and those that were not and aspirin-treated patients with MI had higher serum TxB2 levels than those without MI (p = 0.005).