I'd like to detect the users heart beat but im not sure if Tizen (the mobile O/S by samsung) can detect heart beats. with samsung gear i found this SO article: Get Heart Rate from "Sensor" Samsung Gear Live but i need it with Tizen, any ideas ?
Yes, you can detect user heart rate with Tizen based Samsung gear devices. FYI all Samsung gear devices released till now except gear live are Tizen based.
Have a look at this link on how to monitor heart rate https://developer.tizen.org/fr/development/guides/web-application/tizen-features/system/human-activity-monitor?langredirect=1
You can use the Heart rate monitor sensor which is available on the gear.
Check this link on how to code https://developer.tizen.org/dev-guide/2.4/org.tizen.web.apireference/html/device_api/wearable/tizen/humanactivitymonitor.html