Purpose: To study in vivo radiofrequency (RF) heating produced due to power deposition from a 3T (Larmour frequency=123.2 MHz), birdcage, whole body coil. Methods: The RF heating was simulated in a digital swine by solving the mechanistic generic bioheat transfer model (GBHTM) and the conventional, empirical Pennes bioheat transfer equation for two cases: 1) when the swine head was in the isocenter and 2) when the swine trunk was in the isocenter. The simulation results were validated by making direct fluoroptic temperature measurements in the skin, brain, simulated hot regions, and rectum of 10 swine (case 1: n=5, mean animal weight = 84.0366.85 kg, whole body average SAR = 2.6560.22 W/kg; case 2: n=5, mean animal weight = 81.5966.23 kg, whole body average SAR=2.7760.26 W/kg) during 1 h of exposure to a turbo spin echo sequence. Results: The GBHTM simulated the RF heating more accurately compared with the Pennes equation. In vivo temperatures exceeded safe temperature thresholds with allowable SAR exposures. Hot regions may be produced deep inside the body, away from the skin. Conclusion: SAR exposures that produce safe temperature thresholds need reinvestigation.