A number of animal models have been developed to study both the pathophysiology of heart failure and new therapeutic approaches to this complex syndrome. The most widely used preparations today are the models of rapid ventricular pacing in the dog and myocardial infarction in the rat. Other common approaches include surgically induced pressure or volume overload and toxic myocardial depression. There is no ideal animal model that both perfectly imitates human heart failure and is technically feasible in the laboratory. Each model has advantages and specific limitations, and extrapolations from experimental to clinical heart failure therefore require critical evaluation. Still, animal models have provided new insights into many aspects of the complex pathophysiology of this syndrome and have helped to investigate the efficacy of new therapeutic interventions.