We evaluated the serum levels of IgG antibodies to Helicobacter pylori, Chlamydia pneumoniae and cytomegalovirus and the level of the inflammatory markers C-reactive protein and fibrinogen in 57 patients with acute coronary syndrome, 65 with unstable angina, 60 with stable angina and 44 healthy controls, and whether these markers were associated with cardiac instability 6 months after admission. There was a significant increased risk of late coronary events (cardiac death or readmission with acute coronary events) associated with seropositivity to C. pneumoniae (adjusted odds ratio 2.12; 95% confidence interval 1.16–4.08). Other parameters were not significantly associated with late cardiac events after adjustment for age, sex, diabetes mellitus, hypertension, hyperlipidaemia and smoking behaviour.