Need help in cable temperature calculations
7 milliWatts spread over 60 centimeters will not be detected. 

The heat will be dumped into the chest, and cooled by the blood.

Sunlight is 1,000 watts per square meter, or 1,000 watts per 10,000 square cm.
We easily sense sunlight, which is 0.1 watts per square cm.

Your heat density is 0.1 milliWatts per cm length or about 0.1mW per 1cm*0.2cm
(assuming the insulation spreads out the heat) or about 0.5mw per cm squared.

Thus your heat flux into the skin, thru the wire's insulation, is 200X smaller 
than the sun's flux.