A, 123I‐MIBG H/M at 4 h was significantly diminished in HFrEF and HFpEF compared with healthy controls, with HFrEF showing a more pronounced reduction in sympathetic function than HFpEF. B, The extracellular volume (ECV) fraction, a marker of diffuse interstitial fibrosis was significantly higher in HF patients compared with healthy controls, but there was no significant ECV difference between patients with HF with and without reduced ejection fraction. C, The myocardial ECV correlated inversely with 123I‐MIBG H/M at 4 h (Spearman r=−0.34, P=0.0029), suggesting that ECV expansion reduces sympathetic innervation density, leading to a reduced 123I‐MIBG H/M. D, The adjusted peak Vo
2 was inversely correlated with 123I‐MIBG H/M at 4 h. CMR indicates cardiac magnetic resonance; CPET, cardiopulmonary exercise capacity; HF, heart failure; HFpEF, heart failure with preserved ejection fraction; HFrEF, heart failure with reduced ejection fraction; H/M, heart‐to‐mediastinum; 123I‐MIBG, 123iodine‐meta‐iodobenzylguanidine; Vo
2, oxygen consumption.