Embodiments presented herein provide apparatus and methods for imaging-assisted determination of pressure gradient of blood flow across a valve orifice in a cardiovascular circuit without the use of velocity data measured at the valve orifice. An embodiment of the methods comprise creating an image of a valve orifice, creating a planimeter slice from the image of the valve orifice including a trace of the perimeter of the valve orifice, determining the valve orifice area by determining the area contained within the trace, determining the instantaneous flow rate through the valve orifice based on bulk flow data away from the valve, and determining the instantaneous pressure gradient across the valve orifice from the valve orifice area and the instantaneous flow rate.