VARIABLE g_heading VARCHAR2(2048) ;
declare 
v_result varchar2(100) := 'This is test data';
begin
:g_heading := v_result; 
dbms_output.put_line(:g_heading);
end;

SQL> VARIABLE g_heading VARCHAR2(2048) ;
SQL> declare 
  2  v_result varchar2(100) := 'This is test data';
  3  begin
  4  :g_heading := v_result; 
  5  dbms_output.put_line(:g_heading);
  6  end;
  7  /
This is test data

PL/SQL procedure successfully completed.