Is this battery:
Polymer Lithium-ion Battery
Model Number: PGEB014461
Producing enough energy to power the following Arduino-micro project:
Battery (thin, flexible) to be worn. It will be safely encased (See below)
I would also be using a micro heart pulse sensor module:
https://cdn-shop.adafruit.com/product-files/1093/Pulse+Sensor+Data+Sheet-2018.pdf
and a transmission module
(bluetooth, WiFi, IR, etc... whichever is suggested or judged appropriate for an alpha project(Needs to be reliable for short range))
Edit: Clarifications about safety standards applied and "do not bend" comments...
They do not have to be kept flat. The 0.5 mm cells can be flexed or bent into a cylinder, into a hat band, belt, etc.
As previously mentioned, the battery will be safely encased and will not go against these warnings...
Do not immerse the battery in water or seawater, and keep the battery in a cool dry environment during stands by period.
Do not use or leave the battery near a heat source such as fire or heater.
When recharging, use the battery charger specifically for that purpose.
Do not reverse the position (+) and negative (-) terminals.
Do not connect the battery to an electrical outlet.
Do not dispose the battery in fire or heat.
Do not short-circuit the battery by directly connecting the positive (+) and negative (-) terminal with metal objects such as wire.
Do not transport or store the battery together with metal objects such as necklaces, hairpins etc.
Do not strike or throw the battery against hard surface.
Do not directly solder the battery and pierce the battery with a nail or other sharp object.