php-amqplib - read_write_timeout and heartbeat relation

While reading php-amqplib configuration, I saw two parameters: "heartbeat" and "read_write_timeout".

On the web I found this (on 2 or 3 forums): read_write_timeout must be at least 2x the heartbeat But I never saw the reason behind this.

Can someone explain me why read_write_timeout must be at least 2x the heartbeat? Did it depends on heartbeat interval?

Thank in advance.