The cardiovascular response to exercise has been compared between heart transplant recipients (HTR) and healthy individuals matched to the recipient age. However, no study has compared HTR to donor-age matched controls. Moreover, the cardiovascular response to sustained sub-maximal exercise in HTR requires further evaluation. We therefore examined cardiovascular responses during incremental exercise and sustained (1 hr) sub-maximal aerobic exercise in 9 clinically stable HTR (age: 63 ± 10 yr; VO_2peak: 24.2 ± 10.9 mL/kg/min) and 11 healthy age-matched controls (6 recipient age-matched, RM; age: 60 ± 11 yr; VO_2peak: 36.3 ± 10.7 mL/kg/min, and 5 donor age-matched, DM; age: 35 ± 8 yr; VO_2peak: 51.1 ± 10.4 mL/kg/min). Heart rate (HR) and left ventricular systolic and diastolic volumes (two-dimensional echocardiography) indexed to body surface area (ESVI, EDVI), cardiac output (CI), ejection fraction (EF), systemic vascular resistance (SVRI), end-systolic elastance index (EesI), and arterial elastance index (EaI) were determined. Despite maintained systolic function during incremental exercise, compared to DM controls, HTR had significantly reduced peak CI (6.7 ± 2.4 vs. 11.6 ± 1.4 L/min/m²), secondary to blunted HR, EDVI, and increased peak SVRI. The lower peak CI in HTR compared to RM controls was due to blunted peak EDVI (54.1 ± 13.2 vs. 68.6 ± 5.7 ml/m²). During sustained sub-maximal exercise HTR exhausted their preload reserve, a response that was not fully compensated for by changes in ESVI, HR, or EF. Thus, it appears that HTR are limited by impaired preload reserve, HR reserve and impaired vascular reserve during exercise conditions.