Context: Textbook parameters for thermal ultrasound are based on research using the Omnisound unit. Unique heating rates have been observed among various manufacturers. No studies have been performed regarding heating rates of the Chattanooga Intelect® unit. Objective: Determine the rate of temperature increase of the medial gastrocnemius using the Chattanooga Intelect® Legend XT. Design: 3 x 4 repeated measures factorial design. Independent variables were depth and time. Setting: Research Laboratory. Participants: 25 volunteers (F=14, M=11; age 22.04 ± 2.67). Intervention: Thermocouples were inserted into the medial gastrocnemius at 1.0, 1.75 and 2.5 cm depths. 3 MHz, 1.0 W/cm2 treatment was performed for 15 minutes using the Chattanooga Intelect® Legend XT. Main Outcome Measures: Intramuscular temperature. Results: 1.0 cm heating rate was 0.68°C/min, 1.75 cm had 0.52°C/min rate, and 2.5 cm increased 0.20°C/min. Conclusions: Heating rates varied at each depth and differed from textbook rates. Key words: therapeutic ultrasound, heating rates.