Background Coronary heart disease (CHD) and acute coronary syndrome (ACS) remain significant public health problems. The effect of ACS on mortality and morbidity is largely dependent on the time from symptom onset to the time of reperfusion, but patient delay in presenting for treatment is the main reason timely reperfusion is not received. Objectives We tested the effect of an education and counseling intervention on knowledge, attitudes and beliefs about ACS symptoms and the appropriate response to symptoms, and identified patient characteristics associated with changes in knowledge, attitudes and beliefs over time. Methods We conducted a two-group randomized controlled trial in 3522 people with CHD. The intervention group received a 40 min, one-on-one education and counseling session. The control group received usual care. Knowledge, attitudes and beliefs were measured at baseline, 3 and 12 months using the ACS Response Index and analyzed with repeated measures analysis of variance. Results Knowledge, attitudes and beliefs scores increased significantly from baseline in the intervention group compared to the control group at 3 months, and these differences were sustained at 12 months (p = .0005 for all). Higher perceived control over cardiac illness was associated with more positive attitudes (p < .0005) and higher state anxiety was associated with lower levels of knowledge (p < .05), attitudes (p < .05) and beliefs (p < .0005). Conclusion A relatively short education and counseling intervention increased knowledge, attitudes and beliefs about ACS and response to ACS symptoms in individuals with CHD. Higher perceived control over cardiac illness was associated with more positive attitudes and higher state anxiety was associated with lower levels of knowledge, attitudes and beliefs about responding to the health threat of possible ACS.