This study was conducted to determine the cardiovascular effects of 15 minutes of hot tub immersion at 39 degrees C. Five college-age subjects (4 males and 1 female) volunteered to participate in this study. Assessments were made while sitting first in a chair for 5 minutes and then in the hot tub for 15 minutes. Oxygen consumption (VO2) and cardiac output (Q) measurements were made using a Medical Graphics CPX/D metabolic analyzer. Cardiac output was determined at minute 15 using the indirect CO2 rebreathing procedure. The data were analyzed using the analysis of variance with repeated measures, which indicated that at minute 15, heart rate (HR) and Q were increased, which increased VO2. The increase in Q was due to the heart rate (HR) response and the decrease in systemic vascular resistance (SVR). Mean arterial pressure (MAP) and systolic blood pressure (SBP) were decreased while double product (DP) was increased. There were no changes in stroke volume (SV) or arteriovenous oxygen difference (a-vO2 diff). These findings indicate that the HR and Q responses are necessary to the increase in metabolism (VO2). Hot tube use within these time and temperature constraints should reduce concern over hot tub safety in college-age subjects.