C# Definition:

[ComImport]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
[Guid("00000002-0000-0000-C000-000000000046")]
interface IMalloc {
    // Allocate a block of memory
    // Return value: a pointer to the allocated memory block.
    [PreserveSig]
    IntPtr Alloc(
       [In] UInt32 cb); // Size, in bytes, of the memory block to be     
             // allocated.

    // Changes the size of a previously allocated memory block.
    // Return value: reallocated memory block
    [PreserveSig]
    IntPtr Realloc(
        [In] IntPtr pv,  // Pointer to the memory block to be reallocated
        [In] UInt32 cb); // Size of the memory block, in bytes, to be
             // reallocated.

    // Free a previously allocated block of memory.
    [PreserveSig]
    void Free(
        [In] IntPtr pv); // Pointer to the memory block to be freed.

    // This method returns the size, in bytes, of a memory block
    // previously
    // allocated with IMalloc::Alloc or IMalloc::Realloc.
    // Return value: The size of the allocated memory block in bytes.
    [PreserveSig]
    UInt32 GetSize(
        [In] IntPtr pv); // Pointer to the memory block for which the size is
            // requested.

    // This method determines whether this allocator was used to allocate
    // the specified block of memory.
    // Return value: 1 - allocated 0 - not allocated by this IMalloc Instance.
    // -1 if DidAlloc is unable to determine whether or not it allocated the memory block.
    [PreserveSig]
    Int16 DidAlloc(
        [In] IntPtr pv); // Pointer to the memory block

    // Minimizes the heap by releasing unused memory to the operating system.
    [PreserveSig]
    void HeapMinimize();
    }

VB Definition:

<Runtime.InteropServices.ComImport()> _

<Runtime.InteropServices.InterfaceType(Runtime.InteropServices.ComInterfaceType.InterfaceIsIUnknown)> _

<Runtime.InteropServices.Guid("00000002-0000-0000-C000-000000000046")> _

Public Interface IMalloc

    ''' <summary>
    ''' Allocate a block of Memory.
    ''' </summary>
    ''' <param name="cb">Size, in bytes, of the memory block to be allocated.</param>
    ''' <returns>Returns a pointer to the allocated memory block.</returns>
    <Runtime.InteropServices.PreserveSig()> Function Alloc(ByVal cb As UInt32) As IntPtr

    ''' <summary>
    ''' Changes the size of the allocated memory block.
    ''' </summary>
    ''' <param name="pv">Pointer to the memory block to be reallocated.</param>
    ''' <param name="cb">Size of the memory block, in bytes, to be reallocated.</param>
    ''' <returns>Returns the reallocated memory block.</returns>
    <Runtime.InteropServices.PreserveSig()> Function Realloc(ByVal pv As IntPtr, ByVal cb As UInt32) As IntPtr

    ''' <summary>
    ''' Free a previously allocated block of memory.
    ''' </summary>
    ''' <param name="pv">Pointer to the memory block to be freed.</param>
    <Runtime.InteropServices.PreserveSig()> Sub Free(ByVal pv As IntPtr)

    ''' <summary>
    ''' This method returns the size, in bytes, of a memory block previously allocated with IMalloc::Alloc or IMalloc::Realloc.
    ''' </summary>
    ''' <param name="pv">Pointer to the memory block for which the size is requested.</param>
    ''' <returns>Returns the size of the allocated memory block in bytes.</returns>
    <Runtime.InteropServices.PreserveSig()> Function GetSize(ByVal pv As IntPtr) As UInt32

    ''' <summary>
    ''' This method determines whether this allocator was used to allocate the specified block of memory.
    ''' </summary>
    ''' <param name="pv">Pointer to the memory block.</param>
    ''' <returns>1 - allocated 0 - not allocated by this IMalloc Instance.</returns>
    <Runtime.InteropServices.PreserveSig()> Function DidAlloc(ByVal pv As IntPtr) As Int16

    ''' <summary>
    ''' 'Minimizes the heap by releasing unused memory to the operating system.
    ''' </summary>
    <Runtime.InteropServices.PreserveSig()> Sub HeapMinimize()

End Interface