Figure 1.

Increase in beat rate during the course of heart development. During mouse development, cardiac contractile activity starts at approximately embryonic day 8.0 at roughly 30 beats per minute (bpm) and increases in the adult mouse to 600 bpm. The dotted box shows the rapid increase in rate of contraction during the onset of cardiac function from cardiac crescent stages 1 through to the linear heart tube, roughly a 12-hour period from approximately E8.0 to E8.5. The images show, to scale, an embryo at E8.0 (at left, cardiac crescent in red) and an isolated adult mouse heart (at right). (LHT) Linear heart tube.