Friend, when we see bloody stool this is a sign of inflammation in the colon (large intestines) which can be the result of a primary disorder in the gastrointestinal tract or secondary to a systemic disease. Unfortunately, without a hands-on examination, I will not be able to pinpoint the exact underlying cause, I am sorry. But, common causes are dietary indiscretion, ingestion of a foreign body, infections or even part of a systemic disease. The fact that she has a history of heart disease we need to also consider her heart as a possible cause. For this reason, I would strongly recommend having her checked today by your veterinarian for a hands-on examination. In the meantime, this is what you can do:
1- Do not give things like Pepto Bismol or Imodium.
2- Change her diet to rice (75%) and boiled boneless chicken or ground beef (25%) until the stool is back to normal then wean her back into her regular diet.
3- Supplement with a probiotic, these are friendly bacteria that help with regularity and inflammation. You can buy this over the counter in any pet store.
4- Follow up with your family veterinarian for a hands on examination.
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