Inclusion Criteria:  General inclusion criteria: patients should be able to exercise on a treadmill or a bike, willing to consent to the study procedures and willing to return to site during the follow up period of 72 hours for repeated blood and urine collection  Specific inclusion criteria:  Group 1: Subjects must be at least 60 years of age and meet the master athlete definition of: athletes engaged in cycling ≥8 hours per week or running ≥6 hours per week or triathlon training (combination of swimming, cycling, running) ≥8 hours per week, or equivalent sports activities, for at least 6 months prior to enrollment. Group 2: Genotype positive (G+) cardiac phenotype negative (P-) patients with variant ATTR (i.e. carriers without evidence of disease) Group 3: Patients with ATTR CA who have not been on a stabilizer (tafamidis) within the last 14 days prior to enrollment.  Exclusion Criteria:  Taking diflunisal or daily non-steroidal anti-inflammatory drugs (NSAIDs) use within 2 weeks.