The "heart" of most Win32 applications is the WinMain() function, which calls GetMessage() in a loop. GetMessage() blocks until a message, or "event", is received (with function PeekMessage() as a non-blocking alternative). After some optional processing, it will call DispatchMessage(), which dispatches the message to the relevant handler, also known as WindowProc. Normally, messages that have no special WindowProc() are dispatched to DefWindowProc, the default one. DispatchMessage() calls the WindowProc of the HWND handle of the message (registered with the RegisterClass() function).