I do not know what this particular technique is called but it is common what you are doing. I don't necessarily feel it in my heart moreso then just deep in my chest. My chest is always heavy and I get shooting pains in it sometimes.
I have heard from 2 of my therapists and other people that when you acknowledge the fear and you stop fighting it, it will help to calm yourself. When you fight the fear and you say in your head "oh no, I feel it again, what is that, am I going to die, am I going to have a heart attack, am I going to have another panic attack, please not now, I can't have one right now no no no etc etc" it feeds the fear all of those reactions to panic and anxiety only causes the body more stress and anxiety and causes it to panic more. When we are panicking are bodies tense up including all of our muscles. Some parts of our bodies are effected moreso and others not so much. After I have an attack or after a drive in the car (driving is the worst for me with my panic) I honestly get soar. I try to give myself soft massages as to help release some of those muscles that are so tight and tense. It's almost the same thing as comparing the tense soar muscles from a panic attack to running a mile without stretching afterward...
During one of my hardest times with my panic disorder my therapist told me "I know this is going to sound crazy to you and I know that this is going to be a very scary thought for you, but next time you feel a panic attack coming on or the symptoms of one, try to get as comfortable as you can, sit down in a chair, lay down on your bed, whatever feels best to you and analyze your symptoms and what you are feeling. Really try to feel what your panic attack is doing and assure yourself that you know these symptoms, they are not unfamiliar to you and you know what they are, sink into the panic don't run from it because it only feeds into your panic and makes it worse but run towards your panic full speed, say BRING IT ON, tell yourself, 'I'm ready, I'm going to let myself have a panic attack and I'm not going to fight it.' ". When you do this you will find that your panic attack is much less intense and it lasts for a shorter duration then your normal panic attacks. Acceptance in this disorder is key and there is only so much we can learn about this disorder by researching it, there is so much more we can learn about it and how to better help ourselves with it if we ALLOW ourselves to FEEL what is actually happening to us and what helps us.
I think what you are doing is this and this is why you are feeling some release. I think you should keep with it. Don't ever give up!
I also think I'm going to post part of what I wrote to you in the panic attack forums because I think it can help a lot of other people.
Good luck and god bless