With the purpose of studying coronary collateral circulation and if it has influence in manifestations, complications, prognosis and mortality in patients with ischemic heart disease, we studied 52 patients, 41 male and 11 female, mean age 56 years, who died. All of them had a complete medical record and were seen with regularity until death. They had good quality coronaragraphy and ventriculography. Post-mortem study was done in all of them. They were placed in two groups: group I (27 patients) who had adequate collateral circulation and group II (25 patients) without adequate collateral circulation. We found that group I patients had angina more frequently prior to myocardial infarction (p less than 0.005) with greater duration (30 months). Complications during the acute phase of myocardial infarction were more common in patients without collateral circulation (p less than 0.001). Although we did not find statistically significant differences, we could observe that patients without adequate collateral circulation have less survival, disturbances in ventricular wall mo-motion are more frequently found and there is more incidence of sudden death. There was no significant difference between the apparition of myocardial infarction in patients with or without adequate coronary collateral circulation. Diabetic patients had less collateral circulation than non diabetics (p less than 0.05). We conclude that the protective role of collateral circulation in ischemic heart disease is established, diminishing complications during acute myocardial infarction and providing for longer survival.