Thrombolytic therapy reduces mortality and improves ventricular function in acute myocardial infarction. We review the short-and long-term effects of reperfusion after acute myocardial infarction on left ventricular function and heart failure. The beneficial effects of reperfusion may be achieved by immediate limitation of infarct size or through delayed improvement in ventricular remodeling. Infarct size is dependent on the area at risk, the time delay to reperfusion, the completeness and persistence of reperfusion, and collateral blood flow. The main prognostic parameters after myocardial infarction are vessel patency, infarct size, and ventricular volume and function. Initial infarct size and patency of the infarct-related artery are independent predictors of ventricular volume and function, as well as of survival in the long-term following acute myocardial infarction. The beneficial effects of a patent infarct-related artery are only evident if normal flow is achieved and maintained, and are dependent on the degrees of the residual stenosis. Thrombolyric therapy reduces the incidence of in-hospital congestive heart failure, and this improvement is sustained for at least 5 years. As only a fraction of patients with acute myocardial infarction currently receive thrombolytic therapy, heart failure after myocardial infarction can be reduced by administering thrombolytic therapy earlier to more patients with evolving acute myocardial infarction.