connecting two arduinos via serial tx/rx

If I am only interfacing two arduinos can I simply connect the to each other via the tx and rx lines?

If so, do I need any external hardware or just wires between them (e.g. tx0->rx1 tx1->rx0)

and then I can send messages from one arduino to the other via the normal serial.print method?

I was planning to use I2C but I am short on pins and implementing I2C will cause me to shift around a lot of stuff. My communication is pretty simple as well and is unidirectional. i.e. The master arduino is sending short messages to the slave but not vice versa.

sounds like it'l work fine, just make sure you connect their grounds together.