A tool was developed to assess attitudes of patients with cardiac disease toward performing prescribed behaviors of their medical regimen. Two groups of subjects with heart disease were used to examine validity and reliability of the Miller Attitude Scale. One group included 480 members of Mended Hearts, Inc., and the second group consisted of 35 patients diagnosed with a first myocardial infarction. The second group repeated the attitude scale six months post-hospitalization. Performance of the medical regimen by this group was verified at the six-month follow-up period. Using Spearman Rank Correlation, there was a significant relationship between attitudes and adherence behaviors for three of the five subscales. Alpha reliabilities revealed a high degree of internal consistency of scale items for all five subscales when testing both groups.A factor analysis resulted in eight factors accounting for the majority of the variance. Each of the five behaviors of the medical regimen clearly defined a factor supporting use of the Miller Attitude Scale for assessing attitudes of heart patients toward behaviors of their medical regimen.