Current guidelines recommend that cardiology trainees participate+ in a minimum of 100 cardiac catheterization procedures during their clinical training (volume minimum level 1 training). To examine the differences in case mix seen by cardiology trainees during their training in cardiac catheterization, we examined the first 100 cases done by two trainees at different hospitals. One hospital was a high-volume center performing > 5500 procedures/year, and the other was a low-volume center performing < 1500 procedures/year. Demographic and clinical characteristics of the patients undergoing cardiac catheterization were similar at the two hospitals. Indications were also similar, with the only exception being a higher rate of urgent/emergent cases among patients seen at the low-volume center (8% vs 1%). Minor differences in procedural techniques were present at the two hospitals, with the trainee at the high-volume center having more experience with arm cases (4% vs 0%) and left ventriculograms (77% vs 48%) and the trainee at the low-volume center having more experience with right-heart catheterizations (36% vs 11%) and temporary pacing wires (5% vs 2%). Neither trainee had significant experience with valvular or adult congenital heart disease (2%, low-volume center; 1%, high-volume center). These results suggest that current volume minimums may ensure relatively uniform case mix among physicians who are training in cardiac catheterization at different centers. However, training may be deficient in several areas such as valvular heart disease, congenital heart disease, and arm cases.