ArcGIS Pro 2.3 API Reference Guide
SetLockedAspectRatio Method
Example 

ArcGIS.Desktop.Layouts Namespace > Element Class : SetLockedAspectRatio Method
Double
Sets the locked aspect ratio value of the element. This method must be called on the MCT. Use QueuedTask.Run.
Syntax
Public Sub SetLockedAspectRatio( _
   ByVal lockedAspectRatio As Boolean _
) 
public void SetLockedAspectRatio( 
   bool lockedAspectRatio
)

Parameters

lockedAspectRatio
Double
Exceptions
ExceptionDescription
This method must be called within the lambda passed to QueuedTask.Run.
Remarks
When set to true, this means if element width is set, then the element height will be automatically adjusted appropriately. The same is true if height were modified, then width would automatically be adjusted.
Example
//Modify an element's aspect ratio. 

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  bool elmLocked = element.GetLockedAspectRatio();
  elmLocked = false;  //Turn off the locked state.

  element.SetLockedAspectRatio(elmLocked); //You don't have to get to set; a shortcut would be: element.SetLockedAspectRatio(false);
});
Requirements

Target Platforms: Windows 10, Windows 8.1, Windows 7

See Also

Reference

Element Class
Element Members