When you work out it helps clear your thoughts and think of nothing. It makes you feel good.
The type of heat that the Sun emits is called UV (Ultra Violet) rays. This is a natural type of heat, but it can also be dangerous if you expose yourself to too much UV heat, causing "sunburns", or even skin cancer.
Gap junctions in the intercalated discs allow impulses to be spread across the heart more quickly. This is because gap junctions allow particles/signals to pass through, thus making cells with gap junctions more able to interact.
One more thing—you posted this in the physics section rather than biology.
