The siesta habit has recently been associated with a 37% reduction in coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep. Nevertheless, epidemiological studies on the relations between cardiovascular health and siesta have led to conflicting conclusions, possibly because of poor control of moderator variables, such as physical activity. It is possible that people who take a siesta have different physical activity habits, e.g. waking earlier and scheduling more activity during the morning. Such differences in physical activity may mediate different...