Background: Facilitating radial artery cannulation is important among patients undergoing cardiac catheterization. The aim of this study was to evaluate the efficacy of periarterial injections of nitroglycerin by inexperienced operators in facilitating radial artery cannulation. Method: This randomized clinical trial study was conducted on patients who underwent transradial cardiac catheterization for coronary artery disease evaluation. The patients were randomly divided into 2 groups: Group I was the control and Group II received an additional 500 μG of nitroglycerin subcutaneously. The procedure was done by cardiologists trained for the fellowship of interventional cardiology (inexperienced operators). All the participants were monitored for the occurrence of radial artery spasm, number of punctures before successful cannulation, and the radial artery access time. Results: After the exclusion of 16 patients, 144 patients (118 men and 26 women) at an average age of 55.7 ± 10.2 years were randomly divided into 2 groups: Group I (control, n = 73) and Group II (n = 71). The number of punctures before cannulation was markedly lower in Group II than in the control group (1.9 ± 0.64 vs 2.2 ± 1.04; P = 0.045). The radial artery access time was shorter and radial artery spasm was less prevalent in Group II, but these parameters were not statistically significantly different between the 2 groups. Conclusions: Periarterial injections of nitroglycerin (500 μG subcutaneously) by inexperienced operators significantly reduced the number of punctures during transradial cardiac catheterization. (Iranian Heart Journal 2017; 18(4):6-11)