How to exit/abort from a function that returns VOID?

HI,

I have a PLPgSQL function that return void but I need to exit the function
if some condition returns true.

I have tried to do this, but I got an error:

[code]
IF pVAL_CHAVE_2 > pVAL_CAMPO1 THEN
RAISE NOTICE 'O campo data fim tem de ser maior que o campo data
inicio.';
RETURN 0;
END IF;
[/code]

The error is the folowing:

[quote]
ERROR: RETURN cannot have a parameter in function returning void at or near
"0" at character 1973
[/quote]

My question. How can I display the NOTICE and exit the function?

Best Regards,