| Septum primum | |
|---|---|
 The developing human heart, at day 30. The septum primum (top middle) grows down to separate the primitive atrium into the left and right atrium of the human heart. | |
| Details | |
| Carnegie stage | 13 |
| Days | 29 |
| Gives rise to | atrial septum |
| Identifiers | |
| Latin | septum primum |
| Anatomical terminology | |
During heart development of a human embryo, the single primitive atrium becomes divided into right and left by a septum, the septum primum. The septum primum (from Latin 'first septum') grows downward into the single atrium.