This is a prospective, multicenter observational, unblinded, longitudinal cohort study. Subjects will be enrolled into the study prior to or at the time of heart transplantation. All subjects will follow the center's standard of care surveillance schedule. Blood samples will be collected for Prospera testing at the time any surveillance or for-cause testing, which may include endomyocardial biopsy (EMB), echocardiography or other cardiac imaging studies, and/or molecular testing, is performed.

Subjects will undergo surveillance monitoring for rejection per the institution's standard clinical care schedule after transplant. Surveillance procedures may include EMB, imaging such as echocardiography, and/or molecular testing. Surveillance is expected to occur at this approximate schedule during the 12 months post-transplant:

• Weekly during month 1
• Every other week months 2-3
• Monthly during months 4-6
• Every 1-3 months during months 7-12

For-cause testing for rejection will be performed as clinically indicated and per the institution's standard clinical care. Prospera testing will be performed at the time each standard of care (SOC) rejection surveillance procedure and at the time of each for-cause testing for rejection. Prospera test results will be provided to the clinical team.

Additional blood samples for research only will be collected at the time of each Prospera blood sample collection. Results of testing performed on research blood samples will not be returned to investigators for use in clinical care.

Study central laboratory or central review for research purposes will include:

1. Central pathology review (all EMBs, includes for-cause EMBs).
2. Central echocardiography review at day 30 (± 14 days), month 6 (± 30 days) and month 12 (± 30 days) post-transplant.
3. Central testing of PRA/DSA pre-transplant (between enrollment and transplant), at day 30 (± 14 days), month 6 (± 30 days) and month 12 (± 30 days) post-transplant.

Central pathology and echocardiography review will be performed using uploaded images obtained from procedures performed as part of routine clinical care. Central pathology review, central echocardiography review and central laboratory PRA/DSA are for research purposes; these data will be reviewed during the analysis phase of the study and results will not be returned to investigators for use in clinical care.

The study period will start at enrollment and conclude with the final visit at 12 months +/- 30 days post-transplant.

This study will generate additional preliminary data to be used in the design and implementation of a subsequent confirmatory clinical utility trial.

The primary objectives are to:

1. Describe the association between Prospera dd-cfDNA measures and other diagnostic tests used to detect heart allograft rejection and/or injury, including histology, echocardiography and DSA, in the first post-transplant year
2. Inform rates of clinical outcomes in a contemporary cohort of adult heart transplant recipients to determine power for a future randomized, controlled clinical trial.

The secondary objectives are to determine:

1. The performance characteristics of the Prospera dd-cfDNA assay to discriminate biopsyproven acute rejection (AR).
2. The performance characteristics of the Prospera dd-cfDNA assay to discriminate acute cellular rejection (ACR).
3. The performance characteristics of the Prospera dd-cfDNA assay to discriminate antibody mediated rejection (AMR).
4. The association between dd-cfDNA levels and donor specific antibodies.
5. The association between dd-cfDNA levels and allograft dysfunction as measured by echocardiography.
6. The association between dd-cfDNA levels and allograft hemodynamics as measured by right heart catheterization.
7. The association between dd-cfDNA levels and future adverse clinical outcomes.
8. The effect of treatment for rejection on dd-cfDNA.
9. The variability of dd-cfDNA by patient characteristics, including race and gender.
10. The variability of dd-cfDNA across donor-recipient characteristics, including gender and race mismatch.
11. The association between dd-cfDNA (fraction and absolute level) and predicted heart mass.
12. The association between dd-cfDNA levels and time since transplant.
13. The association between dd-cfDNA levels and rejection with hemodynamic compromise (requiring inotropes and/or mechanical circulatory support).
14. The association between dd-cfDNA levels and incidence of cardiac allograft vasculopathy at one year.
15. The association between dd-cfDNA levels and different regimens of immunosuppression

Inclusion Criteria:

1. Age 18 years or older at the time of signing informed consent.
2. Undergoing transplant evaluation or currently on the heart transplant waiting list and expected to receive a heart transplant.
3. Able to read, understand, and provide written informed consent.
4. Able and willing to comply with the study visit schedule, study procedures, and study requirements.

Exclusion Criteria:

1. Concurrent multiple solid organ or tissue transplants.
2. Prior history of any organ or cellular transplantation.
3. Pregnant.

Heart transplant rejection