Background: Percutaneous coronary intervention (PCI) is currently the most common intervention for cardiovascular disease. Standard care after PCI typically involves a period of bed rest in the supine position, but this position creates voiding difficulties. Objective: This study aimed to determine whether a modified supine position could facilitate bladder emptying after PCI. Method: A randomized controlled trial involving 300 patients was conducted. Patients in the intervention group were nursed in the supine position with the bed tilted 20 degrees upright and with a pillow between their feet and the end of the bed. Patients in the control group received standard care, which was supine positioning. Results: One hundred fifty patients were allocated to the intervention group (100 men, 50 women), and 150 were allocated to the control group (103 men, 47 women). Baseline data did not differ between the 2 groups. Patients in the intervention group had significantly better bladder function as evidenced by a shorter time to the first void (5 vs 15 minutes) and fewer patients requiring voiding assistance (8.6% vs 35.3%). Residual urinary volumes were also much lower in the intervention group (88.71 vs 248.22 mL, P < .001). Conclusions: This study demonstrates that a modified supine position can reduce the incidence of impaired micturition and the preservation of normal bladder function after PCI.