The only food on the O diet which would be generically "heart-unhealthy" would be red meats and other animal proteins. Unlike the Atkins diet (to which the O diet is sometimes uncorrectly linked with) other high fat foods are not recommended. With regard to using animal proteins, I make the point in several places in the book that the current agribusiness meat is not acceptable, and that O's should find sources of free range meats. These meats are naturally lower in fat, as they are not fed grains (a good organic rancher can produce beef with the overall fat content of skinned poultry). It is this type of animal protein that the type O ancestors consumed, not the marblized garbage that we call red meat. Buffalo, which is now widely available, is another good choice.
The other foods on the O diet, such as fish, poultry and vegetables would not be a problem, and the only other food though to be a factor in heart disease, dairy, is not recommended for type O.
As it says in the book, even under less than ideal (ie non-organic meat) O's have a less than average chance of complications such as heart disease (unless they eat a lot of carbohydrate) as they possess an enzyme (intesinal alkaline phosphatase) which helps them break down cholesterol in the diet better than the other types. They also have, by virtue of different levels of clotting factors, slightly thinner blood overall.
It is interresting to note that the Inuit Eskimos, held out as a paradox of nutrition because their high protein and fat diet does not seem to promote heart disease as much as in western populations, are literally 99% type O blood.
When these dietary practices are examined in western societies we see a different outcome. This is undoubtably because we are now factoring in approximately 40% type A's, who are indeed very negatively impacted by this type of diet.