Board has also RX0 TX1 pins.
It has the usb port, which think it uses RX1 TX0 as default TTL output.
If you actually have one of these - http://arduino.cc/en/Main/ArduinoBoardNano - please explain where the RX0/TX1 pins are. The Nano, being 168/328 based, only has a single hardware serial port, connected to the pins marked D0RX and D1TX. You could use SoftwareSerial if you wanted additional serial IO.
So... Serial.print() is using this pins by default?The Tx LED shouldn't blink?