Background: Diagnostic cardiac catheterization is a common procedure in coronary artery disease.Patients’ movement and activities are limited because of potential risks; therefore, they need bed rest. The current study aimed at investigating the impacts of changes in body position and earlier ambulation on comfort, bleeding, and ecchymosis after the diagnostic cardiac catheterization.Methods: The current clinical trial with quasi-experimental design included 90 patients undergoing diagnostic catheterization hospitalized in Shariati Hospital, Tehran, Iran. The purposive sampling method was used in the current study and subjects were allocated into 2 groups of intervention and control each of 45. The control group received the routine practices, the supine and flat rest for 8 to 24 hours, and sandbag for 8 hours. The intervention group changed their position in bed; first hour in flat position and head of bed in 15° and second hour in flat position and head of bed in 30°; then, in the 3rd hour in 45° position as well as applying sandbag on catheter entrance site for the first 3 hours; then, the patient was allowed to rest in any position (15° to 30°). Levels of comfort as well as the amount of bleeding and ecchymosis were studied immediately after the admission, 6 hours, 24 hours, and 7 days after the catheterization. Then, the results were analyzed using Chi-square and the Mann-Whitney tests with SPSS V.11.5.Results: There was no significant difference in the levels of comfort as well as the amount of bleeding and ecchymosis in early admission between the 2 groups, but the level of comfort was higher in the intervention group than the control group at the hours 6 and 24 after the catheterization (P<0.001); in addition, there were no statically significant difference between the intervention and control groups in the amount of bleeding and ecchymosis at 6 hours, 24 hours, and 7 days after the catheterization (P=0.99).Conclusion: It was observed that patients may be allowed to change their bed position, and they may be ambulated earlier (the sixth hour) after the diagnostic cardiac catheterization.