I think I mentioned to you one night, but one can generally calm the heart and the mind with breathing. I've actually done it in the doctor's office to move my blood pressure down back to normal (I was anxious about a test result) and they were surprised at that second measurement; and everyone knows you can't "will" your blood pressure. Breathe is, as it were, "under" the heart; when breathing calms, the heart calms. But you can't will your heart calm. The heart is "under" the brain; when the lungs calm the heart, the heart calms the mind. I know this sounds crazy, but it really works for me and some other people I know who do it. It's nothing more than long smooth inhales through the nose (5 or 6 count) followed by slow exhales through slightly parted lips (6 or 7 count). There are simple apps or even gifs to get you started.