Making decisions to call emergency assistance to patients is an important dimension of nursing practice. Most usually these decision making situations are uncertain and it is expected nurses rely on past clinical experiences. This study, approved by the ethics committees of both a university and an area health service, aimed to describe nurses' reliance on past experiences and identify associated judgement strategies (heuristics). Thirty-two registered nurses with five or more years experience were interviewed. Main findings were: nurses did use their past experiences and these experiences were used in the form of the three "classic" heuristics, representativeness, availability and anchoring and adjustment. It can be concluded past experiences are intrinsic to decision making and this has implications for both the clinical components of nursing educational programs and staffing allocations made by administrators. Some nurses, however, did not include referral to past experiences in their decision-making accounts which may be a limitation of the study design.