This study involved designing an instrument to estimate self care knowledge levels of post myocardial infarction patients. The instrument subscales were diet, smoking, exercise, signs and symptoms of cardiac distress, medications, stress and high blood pressure. Twenty-six subjects were tested following hospital discharge and again two weeks later. Test-retest reliability was performed to establish stability of the instrument. The preset criterion level of.70 for the total scale was not met. The medication subscale did meet the.70 criterion level. Reliability estimates were conducted to establish internal consistency of the instrument. The preset criterion level of.70 was not met for the total scale; however, the stress subscale did meet the.70 criterion level on the retest. Concurrent validity was estimated by comparing subscale knowledge scores with self report behavior. Point biserial coefficients did not meet the preset.70 criterion levels. These results suggest that reliability and validity estimates in the post myocardial infarction patient population were not statistically significant. (Abstract shortened with permission of author.)