Use the search capability to search for ventricle to find papers where they published the algorithm, since there is nothing in MATLAB (no ventricle-finding function or toolbox).
This is an evergreen question. Please search for "sharing GUI" in this forum to find a bunch of solutions.
The object you have to share is the handle of the AXES object you want to plot in. So get the MainGUI's handle from the SubGUI, use it to obtain the handles struct by GUIDATA, and plot from the code of the SubGUI using the AXES' handle as 'Parent' property.
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