Heuristic thinking can influence human behavior in decisions under risk and uncertainty. In an experimental setting, we study whether emotional activation primes individuals to use the representativeness heuristic and the affect heuristic. We observe the decision behavior of 272 subjects in a computer‐based experiment that differentiates between incidental affect and integral affect. Positive incidental affect and integral affect increase the use of the representativeness heuristic, while negative incidental affect has no effect. Our findings have statistical and economic significance and carry implications for insurance companies and regulators.