The primary purpose of the proposed study is to demonstrate the relationship between leisure-time physical activity and primary cardiac arrest (PCA) in an ambulatory population without previous clinical cardiovascular disease. The research will address a question of particular interest to clinicians, cardiovascular epidemiologists, public health policymakers, and the general public: Is vigorous leisure-time activity protective of primary cardiac arrest? Collection and analysis of case-control data from Seattle and suburban King County, Washington will be used to explore this association. Primary cardiac arrest, as recently defined by the Joint International Society and Federation of Cardiology/World Health Organization Task Force on Standardization of Clinical Nomenclature is a "sudden event, presumably due to electric instability of the heart, where evidence which allows other diagnosis is lacking. If no resuscitation is applied or if resuscitation is unsuccessful, primary cardiac arrest is referred to as sudden death. Evidence of previous ischemic heart disease may or may not be present. If death occured in the absence of witnesses, the diagnosis is presumptive."