Dr. Monroe J. Schlesinger was a pioneer pathologist who developed a method to radiographically visualize the coronary circulation in human hearts at autopsy. Acute and long-term animal studies by Dr. Schlesinger et al led to evidence-based conclusions in humans about many manifestations of coronary disease. Clinical syndromes such as angina pectoris and acute myocardial infarction, the beneficial role of collateral circulation, and the anatomic requisites for congestive heart failure and cardiogenic shock were all defined. Information based on the Schlesinger technique was among the first pathophysiologic incentives to salvage jeopardized ischemic myocardium, and evidence derived from his studies influenced the evolving foundation of modern therapy. Schlesinger's technique was to inject the right and left coronary arteries with a lead-based radiopaque agar. After constant contact with this medium for 12 years, he developed lead poisoning. He then changed the formula by substituting iodide for lead. It is of interest that present angiographic studies use iodinated contrast agents. In conclusion, Monroe Schlesinger's work in defining the coronary circulation in postmortem human hearts laid the foundation for future technical advances to analyze the coronary circulation in the living.