Knowledge, attitudes, and beliefs of persons with ischemic heart disease are important predictors of delay in seeking treatment. We tested the psychometric profile of the Acute Coronary Syndrome (ACS) Response Index, a measure assessing patient knowledge, attitudes and beliefs about ACS symptoms and response, in 3,522 patients. On factor analysis, 21 dichotomous knowledge items loaded onto four factors (alpha .82). In a separate factor analysis, another five items loaded on two attitude factors, and seven items loaded on two belief factors (alpha .76). The scales discriminated between patients previously exposed to medical experts. Scale scores were significantly correlated but without evidence of multicolinearity. Initial tests of reliability and validity support further testing of this new instrument.