There is evidence that if you feed your cat only one type of meat, they have a tendency to develop an allergy to it.Hearts are a good source of Taurine. I think it’s good to alternate proteins from time to time. Chicken is good but I would also feed turkey too. A lot of cats become allergic to chicken. I wonder if that’s because that’s all they are being fed. Are you giving these as treats? Because if it’s their main diet you have to make sure it’s balanced.