A subgroup analysis of the US Physicians' Health Study (PHS) of 333 men with chronic stable angina indicated that aspirin reduced the relative risk of acute MI by 87% (P < 0.001) [26]. The Swedish Angina Pectoris Aspirin Trial involved 2035 patients and found a 34% relative risk reduction in the occurrence of a first MI over a four-year follow-up period in patients receiving 75 mg of aspirin daily, compared with patients receiving placebo [27].
The 2002 ACC/AHA guidelines for chronic stable angina include a class IIa recommendation (the weight of evidence where opinion is in favor of usefulness and efficacy) for prophylactic aspirin therapy to prevent MI and death [28].