The yellow H has 2 numbers A and BC
The SV has 2 numbers also DEF and GH
The cache can be found at N52 06.(A-D-B)CE W000 12.(B+D)(G+2)(H+1)
The Hatley Heart Attack was a loop of 400+ caches starting in Hatley and heading north east up to Toft before heading south, then south west all the way over to Biggleswade before heading back up to Hatley.
The series has gone now because I got made redundant by a bunch of idiots and got a job a long way away!
Check out the BookMark List for a complete list of the entire series plus link caches.