Breast Cancer (BC) is the most frequent cancer, whereas CV diseases such as myocardial infarction (MI) are the leading cause of death. BC and MI share common major risk factors such as obesity. We aimed to analyse the characteristics of women with a history of BC in the setting of acute MI. Among the 2087 consecutive women included between 01/01/2001 and 31/12/2009 in the French regional RICO survey database, 73 (3%) had a history of BC. Each woman with prior BC (n = 73) was matched, with respect to age, with 5 women without prior BC (n = 365). Women with prior BC were 74 (65–80) year old. Time from BC diagnosis to acute MI was 10 (3–16) years. Most BC had been treated by surgery and/or radiation therapy, and 37% had also received hormone therapy. CV risk factors (smoking, obesity), type of MI, acute management and in-hospital complications were similar for the 2 groups. Chronic statin use and admission blood lipids were also identical for the 2 groups. However, median admission CRP levels were lower in women with a history of BC (1.0(1.0–9.8) vs. 5.6 (2.8–13.6) mg/l, respectively, p < 0.001). Strikingly, peak CK and troponin Ic levels, the latter of which reflects infarct size, were dramatically lower, by 40%, and 26%, respectively, in the BC group (310 (136–777) vs. 501 (198–1324) UI/l, p = 0.022 and 9.20 (3.33–19.55) vs. 12.36 (2.77–41.00) μg/l, p = 0.166 respectively). By linear regression analysis, prior BC remains an independent predictor of reduced peak CK (B(SE) = −626.8(260), p = 0.017), even when adjusted for potential confounders (anterior wall location, STEMI, multivessel disease, time to admission). In women currently admitted for acute MI, a non-negligible proportion had prior BC. Women with prior BC had a similar risk profile and lipid levels to those in women without prior BC. However, they were characterized by a lower level of inflammation and smaller infarct size than their counterparts without BC. Further investigations are ongoing to determine whether hormone therapy such as oestrogen receptor modulators could account for the observed effects in this population.