What is the difference between the affect heuristic and the availability heuristic?

Even though the affect heuristic and the availability heuristic are different, they are closely linked. This is because availability occurs not only through ease of recall or imaginability, but because remembered and imagined images come tagged with affect or emotion.

For example, availability can explain why people overestimate certain highly publicized causes of death like accidents, homicides, or tornadoes and underestimate others, such as diabetes, asthma, or stroke. The highly publicized ones are more emotionally charged and, thus, more likely to receive attention.

In other words, the affect heuristic is essentially a type of availability mechanism in which emotionally charged events quickly spring to mind.