The bill only says the rhythm must be detectable. within the gestational sack. It doesn;t say it must be detectable as an audible sound detectable by a stethiscope. Medical sources say there is only a slight flutter in the cells that will eventually become the heart's pacemaker. I already gave a credible link to that. If you have a source that says otherwise, I would like to see it. A slight flutter in a few cells, that can only be detected by ultrasound, and when the structure of the rest of the heart doesen't yet exist is not the same as a viable heartbeat At that point, you can't listen to a heartbeat because there is nothing there but a slight flutter in a few cells.