This study aimed to use ultrasound imaging to investigate the milk ejection characteristics of women during a 10-minute expression using an electric breast pump capable of applying 2 markedly different vacuum patterns. The classic pattern (47 cycles/min) and 3-phase pattern (pre-milk ejection: 120 cycles/min, post-milk ejection: 20 cycles/inin for 2 minutes post-milk ejection then 55-78 cycles/min for 8 minutes) were tested, and the milk expressed was collected in 30-second intervals. Multiple milk ejections (96%) were detected (classic: 3.27 +/- 2.05; 3-phase: 3.72 +/- 1.19) and associated with increases in milk flow. Almost half of the total volume of milk expressed was removed during the first milk ejection (classic: 41.38 +/- 21.48%; 3-phase: 46.72 +/- 26.60%). There was no correlation between the number of milk ejections and both the total volume of milk and percentage of available milk for either pattern. In conclusion, milk ejection characteristics and efficiency of milk expression did not change in response to different expression patterns.