This exploratory study used Diagnostic Content Validity (DCV) and the Clinical Diagnostic Validation (CDV) models proposed by Fehring (1986) to clinically identify and validate the defining characteristics for Alteration in Tissue Perfusion: Cardiac. The literature based Kelly Cardiac Assessment Tool (KCAT) was designed as the data collection tool. The diagnostic content validity of the KCAT was 0.70. Twenty subjects, 18 years old and older were selected from a population who were admitted as inpatients in a southwestern university affiliated hospital. Data were collected through patient interviews, independent nurse assessment, and review of laboratory data. Using the steps described in Fehring's CDV model (1986) one major defining characteristic and 13 minor defining characteristics were clinically validated. The tool CDV score was 0.62. The nursing diagnosis Alteration in Tissue Perfusion: Cardiac was clinically validated and one major and 13 minor defining characteristics were identified.