This study aimed to evaluate the cardiometabolic effects of a home-based lifestyle intervention (LI) in breast cancer survivors (BCSs) during the COVID-19 lockdown. In total, 30 BCSs (women; stages 0-II; non-metastatic; aged 53.5 +/- 7.6 years; non-physically active; normal left ventricular systolic function) with a risk factor for recurrence underwent a 3-month LI based on nutrition and exercise. Anthropometrics, Mediterranean diet adherence, physical activity level (PAL), cardiorespiratory fitness (VO2max), echocardiographic parameters, heart rate variability (average standard deviation of NN intervals (ASDNN/5 min) and 24 h very- (24 hVLF) and low-frequency (24 hLF)), and metabolic, endocrine, and inflammatory serum biomarkers (glycemia, insulin resistance, progesterone, testosterone, and high-sensitivity C-reactive protein (hs-CRP)) were evaluated before (T0) and after (T1) the LI. After the LI, there were improvements in: body mass index (kg/m(2): T0 = 26.0 +/- 5.0, T1 = 25.5 +/- 4.7; p = 0.035); diet (Mediet score: T0 = 6.9 +/- 2.3, T1 = 8.8 +/- 2.2; p < 0.001); PAL (MET-min/week: T0 = 647 +/- 547, T1 = 1043 +/- 564; p < 0.001); VO2max (mL.min(-1).kg(-1): T0 = 30.5 +/- 5.8, T1 = 33.4 +/- 6.8; p < 0.001); signs of diastolic dysfunction (participants: T0 = 15, T1 = 10; p = 0.007); AS-DNN/5 min (ms: T0 = 50.6 +/- 14.4, T1 = 55.3 +/- 16.7; p = 0.032); 24 hLF (ms(2): T0 = 589 +/- 391, T1 = 732 +/- 542; p = 0.014); glycemia (mg/dL: T0 = 100.8 +/- 11.4, T1 = 91.7 +/- 11.0; p < 0.001); insulin resistance (HOMA-IR score: T0 = 2.07 +/- 1.54, T1 = 1.53 +/- 1.11; p = 0.005); testosterone (ng/mL: T0 = 0.34 +/- 0.27, T1 = 0.24 +/- 0.20; p = 0.003); hs-CRP (mg/L: T0 = 2.18 +/- 2.14, T1 = 1.75 +/- 1.74; p = 0.027). The other parameters did not change. Despite the home-confinement, LI based on exercise and nutrition improved cardiometabolic health in BCSs.