As more adults are living into old age, they are predisposed to cardiovascular disease (CVD) and the demand for cardiac rehabilitation is increasing. We aimed to verify predictors of length of stay (LOS) in young (Y) vs older (O) vs very old (VO) CVD patients, admitted to residential cardiac rehabilitation. Patients' demographic and clinical characteristics at admission, as well as Barthel index (BI), Cumulative Illness Rating Scale (CIRS), comorbidity severity/complexity, NYHA classification, left ventricular ejection fraction (LVEF), physical activity level were compared in Y (≤65 years) vs O (between >65 and <76 years) vs VO patients (with an age of ≥76 years) against LOS. In 5,070 consecutively CVD patients were included; they were 1392 Y (38%) 1944 O (35%) 1334 VO patients (27%) and LOS duration was 16±7, 19±9 and 22±10 days, respectively (p<0.0001). In Y, LOS was linked to BI (p=0.000) and to LVEF (p=0.000) at multivariable analysis with area under ROC curve of 0.82, whereas in O, LOS was associated to gender (p=0.013) CIRS severity (p=0.000), BI (p=0.000), LVEF (p=0.000), and in those VO to gender (p=0.004), BI (p=0.000) and medical infusion (p=0.000) at multivariable with ROC curve of 0.83 and 0.74, respectively. In very old patients, a prolonged LOS is related to extra-cardiac conditions. Therefore, we promote a specific cardiac rehabilitation for these patients.