The Swedish concept "trygghet" is multidimensional and includes notions such as security, safety, confidence, certainty and trust. Patients in coronary pain are in special need of "trygghet". In order to study the certainty dimension of the concept the Mishel Uncertainty in Illness Scale, MUIS, was used. This 34 item Likert scale is based on four factors: multidimensional ambiguity, complexity, deficit information and unpredictability. A special Cardiovascular Population Scale is formed by utilising 16 of the items included in MUIS. Patients' experiences of uncertainty were studied in two Intensive Coronary Care Units, in different locations, and with different staffing and nursing routines. There were almost no significant differences in scores on MUIS between the two ICCU wards. In the background data, the only discriminating factor was the time between previous and current hospital stays. The shorter the time, the more the uncertainty.