The present invention relates to a method and apparatus for simulating blood flow through a cardiovascular structure, e.g. a blood cavity such as the left ventricle outflow tract, the aortic root including the AV, plus ascending aorta, a ventricle volume, the aorta or any other cavity where blood flows through, under patient-specific boundary conditions derived from the cardiac ejection output per heart stroke. The cardiac ejection output can be estimated from volumes of a heart chamber of the patient in different filling states at two or more different points in time. The results of the flow simulation can be used to derive at least one physiological parameter or can be visualized and virtual Doppler ultrasound images may be generated to allow a physician assessing the result.