1. A system for determining information for a patient, the system comprising: at least one computer system configured to: receive data describing a geometry of at least a portion of the patient's heart; determine a three-dimensional model representing the geometry of at least the portion of the patient's heart based on the received data; identify a cardiac event and a blood flow characteristic threshold value associated with the cardiac event; determine a physics-based model of blood flow through the three-dimensional model simulated at a selected level of physical activity of the patient, the physics-based model including a resistance to blood flow at the patient's myocardium and the selected level of physical activity being selected from a plurality of physical activity levels; model the flow of blood through the three-dimensional model using the physics-based model of blood flow through the three-dimensional model simulated at the selected level of physical activity; calculate, from the modeled flow of blood through the three-dimensional model simulated at the selected level of physical activity, a value of the blood flow characteristic within the patient's heart at the selected level of physical activity; update the physics-based model of blood flow by reducing the resistance to blood flow at the patient's myocardium through iteratively increasing levels of physical activity; model the flow of blood through the updated physics-based model simulated at a level of the iteratively increasing levels of physical activity that is higher than the selected level of physical activity; recalculate a value of the blood flow characteristic within the patient's heart at the level of physical activity higher than the selected level of physical activity to identify a recalculated value of the blood flow characteristic that exceeds the blood flow characteristic threshold value associated with the cardiac event; determine a maximum level of physical activity, intensity, or exercise for the patient based on the level of physical activity at which the recalculated value of the blood flow characteristic exceeds the blood flow characteristic threshold value associated with the cardiac event; and determine one or more physical activity recommendations for treatment of the patient based on the determined maximum level of physical activity, intensity, or exercise for the patient.