Based on the method of multi-scale space (Pm, Gm) and data surrogating test, time-irreversibility analysis is applied to the heart rate variabilities (HRVs) from different crowds and different states, awake and asleep respectively, of healthy youths. The results show that i) the HRVs of healthy crowed have irreversible dynamics prevailingly, while the irreversibility decreases but does not disappear with aging or heart disease appearing. For example, most (more than 75%) of the congestive heart failure (CHF) patients still have irreversible dynamics; ii) for HRVs of healthy crowd, irreversible dynamics presents the daytime/nighttime rhythms and their significant difference between in daytime and in nighttime. And a stronger irreversibility is detected in nighttime. HRV is generated by the cardiac dynamic system, in which regulations usually perform via multiple feedback loops with different delays. Therefore, in order to arrive at a reliable conclusion, multi-scale strategy and data surrogating test are suggested to serve as the two elements for the detection of time irreversibility in HRV. The proposed method combines these two elements and reaches a conclusion consistent with the conclusions in previous reports.