A system for determining cardiovascular information for a patient, the system comprising: at least one computer system configured to: receive non-invasively obtained patient-specific imaging data regarding a geometry of an anatomical structure of the patient, said anatomical structure including at least a portion of an aorta and at least a portion of a plurality of coronary arteries emanating from the portion of the aorta, and at least a non-invasively obtained measurement relating to a blood pressure of the patient; determine a total resistance to blood flow associated with a total outflow of blood through the plurality of coronary arteries, using the measurement relating to a blood pressure of the patient; create a three-dimensional geometric model representing at least a portion of said anatomical structure of the patient based on the patient-specific imaging data; determine boundary conditions at in- and outflow boundaries of the three-dimensional geometric model, the determining comprising using the determined total resistance and a physics-based blood flow model of blood flow through the coronary arteries to determine boundary conditions, said physics-based blood flow model including at least one lumped parameter model modelling structure downstream of an outflow boundary (i), the lumped parameter model including a resistance (Ri) to blood flow through said outflow boundary (i) of the three-dimensional geometric model; and determine information regarding a fractional flow reserve within the anatomical structure of the patient using the three-dimensional geometric model and the determined boundary conditions, the fractional flow reserve being the ratio of the mean blood pressure downstream of a lesion divided by the mean blood pressure upstream from the lesion. at least one computer system configured to: receive non-invasively obtained patient-specific imaging data regarding a geometry of an anatomical structure of the patient, said anatomical structure including at least a portion of an aorta and at least a portion of a plurality of coronary arteries emanating from the portion of the aorta, and at least a non-invasively obtained measurement relating to a blood pressure of the patient; determine a total resistance to blood flow associated with a total outflow of blood through the plurality of coronary arteries, using the measurement relating to a blood pressure of the patient; create a three-dimensional geometric model representing at least a portion of said anatomical structure of the patient based on the patient-specific imaging data; determine boundary conditions at in- and outflow boundaries of the three-dimensional geometric model, the determining comprising using the determined total resistance and a physics-based blood flow model of blood flow through the coronary arteries to determine boundary conditions, said physics-based blood flow model including at least one lumped parameter model modelling structure downstream of an outflow boundary (i), the lumped parameter model including a resistance (Ri) to blood flow through said outflow boundary (i) of the three-dimensional geometric model; and determine information regarding a fractional flow reserve within the anatomical structure of the patient using the three-dimensional geometric model and the determined boundary conditions, the fractional flow reserve being the ratio of the mean blood pressure downstream of a lesion divided by the mean blood pressure upstream from the lesion. receive non-invasively obtained patient-specific imaging data regarding a geometry of an anatomical structure of the patient, said anatomical structure including at least a portion of an aorta and at least a portion of a plurality of coronary arteries emanating from the portion of the aorta, and at least a non-invasively obtained measurement relating to a blood pressure of the patient; determine a total resistance to blood flow associated with a total outflow of blood through the plurality of coronary arteries, using the measurement relating to a blood pressure of the patient; create a three-dimensional geometric model representing at least a portion of said anatomical structure of the patient based on the patient-specific imaging data; determine boundary conditions at in- and outflow boundaries of the three-dimensional geometric model, the determining comprising using the determined total resistance and a physics-based blood flow model of blood flow through the coronary arteries to determine boundary conditions, said physics-based blood flow model including at least one lumped parameter model modelling structure downstream of an outflow boundary (i), the lumped parameter model including a resistance (Ri) to blood flow through said outflow boundary (i) of the three-dimensional geometric model; and determine information regarding a fractional flow reserve within the anatomical structure of the patient using the three-dimensional geometric model and the determined boundary conditions, the fractional flow reserve being the ratio of the mean blood pressure downstream of a lesion divided by the mean blood pressure upstream from the lesion.