This sheet is one of a series of studies that document the detailed investigations of the heart and lungs conducted by Leonardo during the last years of his life.

The studies and notes on this sheet relate to the valves of the heart, their structure and the flow of blood within them. Leonardo is particularly interested here in the geometric structure of the aortic valve.

The drawing on the upper right illustrates a mould for the making of a glass model of the pulmonary or aortic valve, which Leonardo planned to make. A reference to the construction of a glass model of the heart is found on another sheet also at Windsor, dated 1513.