Hi
You should phone your Insurers to advise them of the situation, just in case you need to claim.
When the policy was taken out, there should not have been any heart related issues, otherwise Insurers could treat this as pre-existing medical and not cover. If heart condition is new and you needed to cancel holiday, you are covered.
You should think about getting a letter from a doctor confirming fitness to travel at the appropriate time. If you travelled against medical advice the Insurers could refuse any claim. If you don't get doctors advice, then go on holiday and there is a problem, this could make the process of claiming more difficult.
When the policy is due for renewal you husband will need to go thorugh medical questions with Insurers and they will assess whether they can cover and the premium. This is a link to the British Heart foundation site with details about various Insurances http://www.bhf.org.uk/living_with_a_heart_condition/recovery/insurance.aspx
huckster