Embodiments are directed to an electronic device having integrated sensors for detecting a user's cardiac electrical signals. The device can include a heart sensor having several leads for detecting a user's cardiac signals. The leads can be coupled to interior surfaces of the device housing to hide the sensor from view, and electrical signals generated by the user can be transmitted from the user's skin through the electronic device housing to the leads. In some embodiments, leads can be coupled to the exterior of the housing. The device can be finished so that the pads are integrated with the device to improve aesthetic qualities of the device. The electronic device can use the cardiac signals to identify or authenticate the user and perform operations based on the identity of the user. In some embodiments, the electronic device can provide data related to the user's mood based on the cardiac signals.