The goal of this observational study is to systematically assess the presence and distribution of CMR-defined inflammation and fibrosis in clinically stable HT recipients with DSA detected during active screening for AMR surveillance. The main outcome is to study the prevalence of fibrosis, edema and of altered T1 mapping values in patients with DSA and the prevalence of patients with DSA among all the enrolled patients

This is a multicentric prospective study with experimental sample collection. Therapy and procedures will be performed according to clinical practice and current guidelines. Caring physicians will be blinded to the results of study specific assays, which will not be used to change standard cynical decision making.

Patients will be enrolled in the study at the time of the DSA assay performed in the context of standard surveillance (yearly monitoring for anti-HLA antibodies is recommended by current guidelines and is part of routine clinical practice). At study entry patients will receive blood sampling to assay dd-cfDNA (centralized laboratory) and T-reg populations (local laboratory). Clinical characteristics, medical history, and results of standard laboratory tests will be collected at baseline.

Inclusion Criteria:

• Age > 18 years

  • Post heart transplantation follow-up between 1 and 15 y
  • Ambulatory clinical stable
  • Left ventricular ejection fraction (LVEF) > 40% (as assessed by complete cardiac ultrasound within 3 months before the enrolment)

Exclusion Criteria:

• Unplanned hospitalization for cardiovascular causes in the previous three months

  • Biopsy-proven cellular (2R or greater) or AMR (pAMR> 1 ) in the previous 3 months
  • Any contraindication to CMR
  • Known pregnancy

Clinically stable adult heart transplanted patients will be consecutively enrolled during the routinely outpatient evaluation in the participating centers after IRB approval.

Heart Failure and Transplant Unit of IRCCS AOUBO will be the project leader and coordinate the overall study. The investigators plan a one year period for the enrollment and eight months for the follow-up.

Patients will be treated and followed according to the routinary clinical practice of each participating center.