Experimental psychology has long demonstrated that task switching imposes cognitive demands and increases error rates, yet its real-world impact in high-stakes work environments remains unclear. Here, we provide the first causal evidence of switching costs in the context of organ transplantation.  Leveraging the effectively random timing of donor-organ arrivals as a natural experiment, we analyze national registry data on 316,743 U.S. transplants from 2007 to 2019. We find that switching organ types (e.g., from liver to kidney) increases one-year post-transplant mortality by 0.66 percentage points, a 14.8%  increase relative to the baseline. These risks can be mitigated through structured scheduling, longer recovery intervals between procedures, and greater surgeon experience.  Our findings identify task switching as a modifiable risk factor in expert performance and offer actionable strategies to improve outcomes in high-stakes settings.