Background:The present study aimed to evaluate the effects a cardiac rehabilitation program (CRP) performed in the morning or evening on left ventricular (LV) filling indices and the level ofN-terminal fragment of pro-brain natriuretic peptide (NT-proBNP) in patients undergoing percutaneous coronary angioplasty during the COVID-19 pandemic.Methods:This was a randomized controlled single-blinded clinical trial. Ninety-six patients (mean age: 50.2 ± 8.1 years, 36 women and 44 men) with percutaneous coronary angioplasty were divided into two groups of intervention and control. In each group, the CRP was performed in either morning or evening. The CRP included walking and performing push-ups and sit-ups for 8 weeks. The participants of the control groups received routine care. The functional indices of LV, including LV ejection fraction, systolic function, and diastolic function (i.e. the transmitral flow), the E/e’ to left atrium peak strain ratio (as an estimation for LA stiffness), and NT-proBNP level were measured in all participants before starting and at the end of the CRP.Results:In the intervention group, the individuals performing the CRP in the evening had significantly higher E-wave (0.76±0.02 vs. 0.75±0.03;P=0.008), ejection fraction (52.5±5.64 vs. 55.5±3.59;P=0.011), and diastolic function velocity (E/A ratio, 1.03±0.06 vs. 1.05±0.03;P=0.014) and significantly lower A-wave (0.72±0.02 vs. 0.71±0.01;P=0.041), E/e’ ratio (6.74±0.29 vs. 6.51±0.38;P=0.038), and NT-proBNP level (2007.9±214.24 vs. 1933.9±253.13;P=0.045) compared with those performing the program in the morning.Conclusions:A supervised CRP performed in the evening compared with morning was more effective in improving LV functional indices. Therefore, such home-based interventions are recommended to be performed in the evening during the COVID-19 pandemic.