RecruitingGenome Transplant DynamicsStudy Description: Heart and lung transplants can save lives, but long-term success is often limited by organ rejection that is hard to detect early. This study is testing a new, non-invasive blood test that looks for small pieces of DNA from the donor organ in the patient s blood. We believe higher levels of this donor DNA may signal early rejection before damage becomes permanent. Hypothesis: We believe that measuring donor-derived DNA in the blood can help detect early signs of rejection and improve outcomes for transplant patients. The study also collects genetic and biological samples to explore why some people are more at risk of complications after transplant. This may help guide future research and treatments. Who Can Join the Study: People receiving a heart or lung transplant (or both), age 14 and older People who are within three months of their transplant People who can understand and agree to take part in the study Participants will be asked to provide blood and other samples, and some of these will be used in lab research to explore new ideas about how and why transplant rejection happens. This research could lead to better ways to monitor and treat patients after a heart or lung transplant - and help improve long-term survival and quality of life.