Theories of an optimal level of arousal suggest that underaroused humans seek stimulation to enhance their arousal. One way to increase arousal is risky behavior during gambling. In the current study, we show that the lower the participants' resting arousal, measured via resting heart rate, the riskier they acted in a gamble and the faster they responded, indicating less impulse control. Participants with low resting heart rate also perceived the risk options in the gamble as less arousing and less risky compared to participants with higher resting heart rate. Partial correlations show that resting heart rate, risk behavior, and ratings were interrelated. After physical exercise, participants tended to behave less risky in the gamble compared to a control condition without exercise. Thus, both trait and state arousal effects indicate an inverse relationship of arousal and risky behavior.