Paul
I'm not aware of any DLA or AA Case Law that references a heart condition, although that doesn't mean it doesn't exist, you can access all of the available Case Law on the following link
www.osscsc.gov.uk/Aspx/default.aspx I would be surprised if you find anything as DLA is based on your Care and Mobility needs, not the underlying condition that causes them, also for most conditions there is a wide variation on the impact that they have, so it would be perfectly possible for two claimants with the same underlying condition, to have one on HRC and MRC and the other not qualifying for DLA at all.
As a general comment in regard to using Case Law, make sure you fully understand what the case applies to, and just as importantly, what it does not apply to.
Gordon
