1. A system for determining cardiovascular information for a patient, the system comprising: at least one computer system configured to: receive patient-specific data regarding a geometry of an anatomical structure of the patient, the anatomical structure including at least a portion of one or more coronary arteries, and the patient-specific data including image data; create a three-dimensional model representing at least a portion of the anatomical structure of the patient using the patient-specific data; determine a myocardial mass of the patient using the patient-specific data; estimate total coronary blood flow of the patient using the determined myocardial mass; create a reduced-order blood flow model relating to a blood flow characteristic within the portion of the anatomical structure based, at least in part, on the estimated total coronary blood flow and the three-dimensional model; create a multi-dimensional model using the three-dimensional model and the reduced-order blood flow model; and determine a value of a fractional flow reserve at each of a plurality of locations within the portion of the anatomical structure using the multi-dimensional model.