Background: Although some investigations have shown higher rates of successful first attempt and fewer attempts by using ultrasound-guided Internal Jugular Vein (IJV) catheterization, arterial puncture is still common. Objectives: The present study aimed to investigate US-guided catheterization of the right IJV via medial-oblique technique and also compare this technique to short-axis technique in open-heart surgery patients. Patients and Methods: In this randomized clinical trial, 80 patients referred to cardiac operating room of Namazi hospital, Shiraz, Iran from March to July 2014 were selected using census method. Block randomization with website was also done. Then, the patients were divided into two groups of 40, Short Axis Group (SAG) and Medial-Oblique Group (M-OG). For short-axis technique, patient’s head was positioned at zero degree angulation with his trunk. For medial-oblique technique, on the other hand, patient’s head was tilted to left to 45 degrees between the head and trunk. Sex, age, Body Mass Index (BMI), access time, guidewire time, cannulation time, total attempts for catheterization, first, second, and third attempt success, arterial puncture, hematoma, bleeding, and catheter malposition were recorded. The overlap between the carotid artery and IJV in zero- and 45-degree angulation was estimated through ultrasound print. After all, Kolmogorov-Smirnov test was used to assess normal distribution of the data. Then, the data were analyzed through Student’s t-test, Mann-Whitney U test, and chi-square test. P < 0.05 was considered as statistically significant. Results: The results showed no significant differences between the two groups regarding the duration of different catheterization steps (P = 0.376). In all the cases in both groups, accessing the vein was successful with three attempts or less. There were no clinical complications of catheterization in the two groups. The mean of overlap was 23.60 ± 33.47 in zero-degree angulation between the head and trunk and 32.72 ± 36.38 in 45-degree angulation and this difference was statistically significant (P = 0.001). Conclusions: The results of the present study showed that both US-guided techniques under investigation had the same duration in different catheterization steps, total success rate, and primary mechanical complications, and could be used in clinics.