The importance of an open heart for meditation

Hello Everyone

I've recently been reviewing my meditation practice and looking back at the methodology in gnosis and have been considering different factors that will help.
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How important is an open heart for meditation?

If meditating with the heart centre cold and switched off will meditation be ineffective?

Also I noticed tonight when I did the relaxation technique PATIENTLY and PROPERLY not only was a deeper state of relaxation induced but the heart started to feel as if it was naturally coming into activity. This reminds me of the quote from Samael Aun Weor;

"Therefore we recommend that you dear reader remember your self on a daily basis and relax your physical body completely on a sofa for a moment (whether it be for five or ten minutes, or for half an hour). Thus one day you will be able to experience the reality in your consciousness. This practice brings the superior emotional centre together with the motor centre into activity, thus, when in complete relaxation, our consciousness experiences the being, feeling him, experiencing him."

So then can relaxing properly be conducive to the opening of the heart?
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Also can indulging in negative forms of music, movies, etc and our own general splurge of negative emotions cause the heart to be switched off?

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Are there any more tips for opening the heart?

Thanks