Talking with Geronta Pavlos of Sinai

Q How can a person stay close to God when not in church, nor at home, where he can pray? For instance, while at work in a stressful environment?

A Monks have discovered a short prayer for this purpose which is easy to use. One can say it from within the heart, not just with the mouth. That is why it is called prayer of the heart, 'Lord Jesus Christ have mercy on me the sinner’. It doesn’t take a lot of effort and it is easy for a person to say from within his heart.

- (Laughing) But the day that he will open his mouth to judge another.. he might as well not even try.. 

That’s the biggest secret.

From http://www.mountsinaimonastery.org/q-a/

(For more on this subject, please see the video Mysteries of the Jesus Prayer (a TV version) in our Video Library.)