While the majority of individuals with coronavirus disease 2019 (COVID-19) recovercompletely, a significant percentage experience persistent symptoms, which has beencharacterized as Long COVID and may be associated with cardiac and autonomicdysfunction. We evaluated heart rate variability (HRV) at rest and during deep-breathing(M-RSA) in patients with Long COVID. Case-control design involved 21 patients with LongCOVID and 20 controls; the HRV was evaluated (Polar® system) at rest in the supineposition and during M-RSA and expressed in time domain and non-linear analysis. We foundthat Long COVID in patients resulted in a reduction HRV measures compared to controls:Supine [Mean_iRR=716.9±948.2 vs 948.2±99.6 p<0.001; STD_iRR=12.7±6.9 vs 45.6±20.7p<0.001; STD_HR=1.7±0.7 vs 3.1±1.2 p<0.001; SD1=6.9±4.1 vs 29.5±14.4 p<0.001;SD2=16.4±9.0 vs 56.7±25.6 p<0.001; alpha2=0.5±0.2 vs 0.7±0.1 p<0.001)]; M-RSA:[Mean_iRR=685.9±97.4 vs 845.3±112.4 p<0.001; STD_iRR=24.8±14.9 vs 95.7±111.8p<0.001; Mean_HR=89.4±12.9 vs 72.8±10.3 p<0.001; STD_HR=3.2±1.3 vs 6.0±2.1p<0.001; rMSSD=14.7±8.7 vs 45.2±19.9 p<0.001; RR_tri-index=6.2±3.4 vs 15.1±3.3p<0.001)]. In conclusion, Long COVID negatively impacted HRV at rest and duringdeep-breathing. These findings may imply impairment of cardiac autonomic control whensymptoms of COVID-19 persist following initial recovery.