BACKGROUND Patients with Parkinson's disease (PD) are physically less active than controls, and autonomic dysfunction may contribute to this sedentary lifestyle. Specifically, an altered cardiovascular response to physical effort may restrict physical activities. OBJECTIVE To assess the cardiovascular responses to a submaximal exercise test in PD patients and controls, 546 sedentary PD patients and 29 sedentary healthy controls performed the Åstrand-Rhyming submaximal cycle exercise test. METHODS Average heart rate was used to estimate maximal oxygen consumption (VO2max). Variables that may affect submaximal activity in PD patients, including disease severity, fatigue, and level of physical activity in daily life, were recorded. RESULTS Fewer PD patients (46%) completed the submaximal exercise test successfully than the controls (86%). The estimated VO2max of patients with a successful test was 34% lower than the controls (p < 0.001). Multivariate regression analyses revealed that higher body weight, lower systolic blood pressure, lower resting heart rate, and lower maximal workload were associated with an increased risk of an inadequate heart rate increase during submaximal exercise (R2 = 27%). PD patients with a successful submaximal exercise test had lower estimated VO2max values than controls. CONCLUSIONS Importantly, half of the PD patients had an inadequate heart rate increase during submaximal exercise, which was likely caused by cardiac sympathetic denervation leading to autonomic dysfunction. PD patients should therefore be screened to identify their limitations in exercise performance. Caution should be applied when prescribing beta blockers, as they might limit physical activities further.