This function closes the current database connection specified by a handle returned from a pg_connect() call.
<?php
    $pgsql_conn = pg_connect("dbname=mark host=localhost");
    if ($pgsql_conn) {
        print "Successfully connected to: " . pg_host($pgsql_conn) . "<br/>\n";
    } else {
        print pg_last_error($pgsql_conn);
        exit;
    }
    if(!pg_close($pgsql_conn)) {
        print "Failed to close connection to " . pg_host($pgsql_conn) . ": " .
       pg_last_error($pgsql_conn) . "<br/>\n";
    } else {
        print "Successfully disconnected from database";
    }
?>
Of course you normally wouldn't print a message.  
Regards, --mark