Large-scale trials have demonstrated a consistent mortality reduction from angiotensin converting enzyme (ACE) inhibitor therapy for chronic heart failure. Nonetheless, the pharmacologic and physiologic mechanisms of this favourable affect and the appropriate target population remain controversial. ACE inhibitors exert vasodilator, neurohormonal inhibiting and growth inhibiting effects that may contribute to the clinical response. They improve pump function and prevent ventricular remodelling, but they also may exert an antiarrhythmic effect. They may prevent coronary ischaemic events but appear to reduce cardiovascular event rates even more in non-ischaemic than in ischaemic heart disease. Their efficacy in early stages of asymptomatic heart disease and the optimal dose of the drugs for long-term benefit require further study.