1. A method for simulating perfusion of the myocardial muscle using computed tomography or computed tomographic angiography, the method comprising: receiving imaging data of at least a portion of a patient's myocardial muscle and one or more coronary blood vessels of the patient's heart; identifying, from the imaging data, different three-dimensional regions of the portion of the patient's myocardial muscle, wherein each three-dimensional region is identified based on a location of an outflow boundary of one of the one or more coronary blood vessels or a branch extending from the one or more coronary blood vessels; generating a three-dimensional model of the portion of the patient's myocardial muscle and coronary blood vessels, using the identified three-dimensional regions from the received imaging data; simulating blood flow through the three-dimensional model and determining, from the simulating, the blood flow into the different three-dimensional regions of the myocardial muscle into which different branches of the coronary blood vessels lead; simulating local perfusion of the myocardial muscle for the different three-dimensional regions of the myocardial muscle from the determined blood flow into the different three-dimensional regions of the myocardial muscle; determining one or more three-dimensional regions of the myocardial muscle that are at risk of insufficient perfusion using the simulated local perfusion of the different three-dimensional regions of the myocardial muscle; and displaying a map of perfusion on the three-dimensional model of the myocardial muscle, based on the simulated local perfusion of the myocardial muscle for the different three-dimensional regions of the myocardial muscle, wherein the map of perfusion displays one or more of the three-dimensional regions, and identifies the one or more three-dimensional regions that are at risk of insufficient perfusion.