Hello, and I hope I can help you today. If your sister-in-law truly is on a heart transplant list, it means her heart function is very compromised. Pregnancy increases strain on a women s heart, and pregnancy also makes blood clot more easily, which can put women at risk for stroke if they have abnormal heart motion. The fact that she needs a pacemaker is another sign that her heart cannot beat properly on it s own. Therefore, I hope your sister-in-law is getting care at a major medical center and can consult with a high-risk obstetrician, because pregnancy may be an extremely risky state for her. There is no danger from maternal heart disease to the baby, but the mother may have an increased risk of stroke, heart attack and even death if the pregnancy continues. So without complete review of all you sister-in-law s medical records, I cannot exactly determine what her percent risks are, but all women with severe cardiac disease while pregnant have an increased risk of death. I sincerely hope her doctors will determine the best course of action for her health, which may be to not continue the pregnancy if that is an option. I hope I was able to help answer your question and sincerely wish your sister in law the best of luck for her health and her pregnancy. Sincerely, Dr. Brown