In situ simulation is a new tool for building teamwork during crisis. However, only a few studies have discussed the long-term effects of regular in situ simulations. To better understand these effects, this study retrospectively analyzed the effect of regular (twice a month over a four-year period) in situ simulations in the National Cheng Kung University Hospital acute care ward, which provides care for patients with acute illnesses and requires admission during an emergency room visit. The simulations were held in a real clinical environment using a low-fidelity mannequin and the trainees involved in the simulations were the medical staff of the acute care ward. In this study, we review the effects of such long-term simulations with respect to team performance based on the Ottawa global rating scale (GRS) and incidences of urgent intubation and unexpected cardiac arrest. Our results revealed that among the 84 simulations that were conducted during the study period, 42 could be categorized as “high performance” and the remaining 42 as “low performance” based on the team’s Ottawa GRS. Further, the seniority of nurse leaders and exposure of nurses to repeated simulations did not have any effect on performance. However, although regular simulations did not have any effect on the number of urgent intubations, they caused a marked decrease in the number of unexpected cardiac arrests. The current study did not show that repeated, low-fidelity, regular in situ simulations improve team performance in simulations based on Ottawa GRS, but it was associated with a reduction in the unexpected cardiac arrest rate in the acute care ward. Our results support the use of in situ simulations in acute care wards as an educational tool for first-line caregivers.