Post-graduate training for physicians involves a high level of stress. High stress during training has the potential to cause burnout, a well-studied phenomenon in medical trainees. Burnout has previously been shown to increase the risk of mental health problems and medical error in trainees. Little research has been done on the impact of stress on new fellows in general and pediatric cardiology fellows in particular; understanding common sources of stress offers the opportunity to design targeted interventions to support trainee wellness. New trainees in Boston Children’s Hospital’s Pediatric Cardiology Fellowship program were asked to answer to the following question at the beginning of their training: “What are you afraid of in the coming year?” A qualitative content analysis was done on their anonymous responses. Responses were coded and analyzed for common themes. The overall analysis found that 83% of fellows reported fear of “fellowship/career responsibilities.” The second most common theme was “failure/disappointment” (78%) followed by “personal life” (74%), “emotional exhaustion” (61%); least common was “new hospital environment” (37%). The most common individual fear was “increased clinical responsibility” reported by 65% of the new fellows, while 62% reported fears of “imposter syndrome,” and 58% about “burnout.” We found that fellows commonly report fears about both clinical and personal responsibilities, similar to stressors found in studies on residency. It is important for pediatric cardiology fellowships to develop early and specific interventions designed to assist fellows in managing both their new clinical responsibilities and their other stressors.