If you have heart disease, you must meet certain criteria to donate blood.
Q. I have heart disease but would like to donate blood. Is it safe?
A. According to the American Red Cross, you can donate blood provided you meet certain criteria and your doctor has not told you to restrict your activity. Wait at least six months before donating if you have an episode of angina, a heart attack, bypass surgery, angioplasty, or a change in your heart condition that resulted in a change to your medications. If you have a heart murmur or have been treated for a heart valve disorder, giving blood is probably safe if you've had no symptoms in the last six months.
Also, your blood pressure can't be too high or too low. The upper limit is 180/100 mm Hg, and the lower limit is 80/50 mm Hg. Taking blood pressure medication does not disqualify you from donating, nor does taking most other drugs used to treat or prevent heart disease. The one important exception is anti-clotting drugs, which are described in the question above. If you're taking any of these drugs, you should not donate because your blood won't clot normally. Even if you meet all the criteria, it's still a good idea to talk to your doctor before donating, and with the person who takes your health history at the time of donation.
— Deepak L. Bhatt, MD, MPH
Editor in Chief, Harvard Heart Letter