Heart imaging may reveal hidden clues in rare heart disease

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Subject is clinically stable without cardio-vascular-related hospitalizations within 6 weeks prior to enrollment as assessed by the investigators. * Subject is able to provide written informed consent and is willing and able to complete study procedures. * Currently in sinus rhythm by clinical assessment or documented electrocardiographic studies. * Subject and disease characteristics noted by medical record review: * Healthy control volunteers must also meet the following criteria: Karnofsky performance scale \> 80%; ECOG status 0 or 1. * ATTR cardiac amyloidosis based on meeting all the following criteria: Diagnosis of amyloidosis within five years prior to study screening; Documentation of absence of AL, heavy chain disease, multiple myeloma or malignant lymphoproliferative disorders; Transthyretin amyloid deposits in cardiac tissue OR technetium (99mTc) pyrophosphate scintigraphy with grade 2 or 3 cardiac uptake OR Transthyretin amyloid deposits in non-cardiac tissue with echocardiographic evidence of cardiac involvement or an end-diastolic mean wall thickness \>12mm OR Transthyretin amyloid deposits in non-cardiac tissue with CMR diagnostic of amyloidosis * AL with cardiac involvement based on meeting all the following criteria: Diagnosis of amyloidosis within five years prior to study screening; Histopathologic diagnosis of amyloidosis with AL protein identification; Documented clinical signs or symptoms consistent with heart failure; Cardiac involvement as defined by: Amyloid deposits in cardiac deposits OR Echocardiography with an end-diastolic mean wall thickness \> 12 mm in the absence of other causes OR Elevated NT-proBNP (\>332 ng/L) in the absence of renal failure or atrial fibrillation OR CMR diagnostic of amyloidosis; * AL without cardiac involvement based on meeting all the following criteria: Diagnosis of amyloidosis within five years prior to study screening; Histopathologic diagnosis of amyloidosis with AL protein identification; No documented clinical signs and symptoms consistent with heart failure from AL; Absence of cardiac involvement as defined by: Echocardiography with an end-diastolic mean wall thickness \< 13 mm if the subject does not have other causes for increased wall thickness AND NT-proBNP \<333 ng/L if the subject does not have renal failure or atrial fibrillation AND No CMR diagnostic of amyloidosis if CMR is available prior to screening. Exclusion Criteria: * Unable to consent or unable to complete all study procedures. * Unable to ambulate for 6 minutes (confirmed at study coordinator visit). * Unable to maintain in supine position for 30 minutes. * Unable to maintain breath-holding for 10 seconds (confirmed at study coordinator visit). * Contraindications for safe CMR scanning (e.g., uncontrolled claustrophobia, cochlear implant, implanted neural stimulator). * Presence of implantable cardiac pacemaker or defibrillator. * History of complex congenital heart disease, intracardiac shunt (except for patent foramen ovale), prosthetic valves, prosthesis in the main pulmonary artery or ascending thoracic aorta. * Significant artifact from prior MRI studies. * Pregnant or breast-feeding women. * Weight equal to or greater than 155 kg. * Maximum body side-to-side or anterior-posterior diameter equal to or greater than 70 cm. * Documented non-sinus rhythm within 1 week prior to screening. * For healthy controls, the following exclusion criteria apply, confirmed per chart review and/or patient report: * History of cardiomyopathy or structural heart disease; * History of valvular disease of greater than mild severity; * History of coronary artery disease or coronary heart disease; * History of cardiac or thoracic surgery. * History of symptomatic, persistent atrial tachyarrhythmia, ventricular tachyarrhythmia, or bradyarrhythmia; * Left ventricular hypertrophy or abnormally increased myocardial thickness by prior echocardiography, cardiac computed tomography, or CMR; * Acute kidney injury, OR chronic renal disease with glomerular filtration rate \< 45 mL/min/1.73m\^2 as per medical record review. * Uncontrolled hypertension of systolic blood pressure \> 150 mmHg or diastolic blood pressure \> 90 mmHg as per medical record review; * Taking three or more anti-hypertensive medications; * Type 1 diabetes, OR uncontrolled type 2 diabetes mellitus of hemoglobin A1c greater than 8, as per medical record review; * Taking three or more diabetic medications; * History of confirmed stroke or transient ischemic attack, as per medical record review; * Current cigarette smoker; * History of plasma cell dyscrasia or chronic malignant hematologic diagnosis; * BMI \> 35 kg/m\^2.