When a conversation becomes difficult, I can return to a more centered, grounded state by asking two questions:
1) What is the purpose of my communication?
2) Will the choices I make serve that purpose?
Let's try it. Think of a conversation that you need to hold but have been putting off because you're concerned that it might not go well. What is your purpose for having the conversation? It helps to have a useful purpose. For example, trying to get the other person to change is not useful. You have no control over that. On the other hand, learning about his experience could be very useful.
What choices could you make to serve this purpose? Listening is a good start, and summarizing to clarify that you both heard the same thing. Asking questions that validate your partner and seek to understand his view also work beautifully. What is your purpose, and what choices will support it?
Other useful purposes could be sharing your experiences, or looking for mutually beneficial ways to solve a problem. Perilous purposes include venting on your partner, or making sure he understands how wrong he is. It sounds silly - who would ever choose such a purpose? But I know I've done it.
One caution: sometimes I think I'm going into a conversation with a useful purpose, like learning, but I find that the feeling or attitude behind it is more about revenge or punishment. So though I use the "appropriate" words, my partner still feels attacked.
Paying attention to your purpose for the conversation will give you the courage to have it and help you to stay grounded when things get hot.