BACKGROUND AND OBJECTIVES: The beneficial effects of systemic thermal therapy such as taking a hot tub or sauna have been described for patients with cardiovascular disease. Despite such positive effects, there is still concern over the safety of these procedures. Half-body immersion has recently been widely used as an alternative to achieve the same benefit, and it is better tolerated than conventional whole-body immersion (WBI). However, there has been no study that has clarified the cardiovascular effect of half-body immersion (HBI). SUBJECTS AND METHODS: We asked 13 healthy men (age : 20 to 27 years) to immerse themselves to the shoulder level on day 1) and to the umbilical level on Day 2 for 20 minutes in a hot tub, respectively (temperature : 39.0 to 41.0degrees C). Changes of skin (TSk) and esophageal temperature (TEo), hemodynamic and autonomic responses, and symptom scale were measured during the immersion. RESULTS: All the volunteers were compliant and there were no adverse events. During immersion, the TEo increased continuously with each methods, but 10 minutes after immersion the TEo for the WBI patients was higher (p=0.03). The heart rate (HR) increased and the diastolic blood pressure decreased for both conditions. In contrast to HBI, the ejection fraction (EF) (p=0.10), and cardiac output (CO)(p=0.005) increased continuously for WHI. Among the HRV parameters, the values for the low-to-high frequency ratio (p=0.03) increased significantly with WHI after 10 minutes. The symptom scale during (p=0.01) and immediate after immersion in the hot tub (p=0.005) was better for HBI. CONCLUSION: Core temperature, echocardiographic systolic parameters and sympathetic activity were increased more slowly for HBI compared to WBI. This suggests that HBI could be a safer alternative for systemic thermal therapy for the patients with cardiovascular disease.