Irregular heart rate becomes more regular during warm water immersion. Velocity time integral from the aortic outflow tract is shown for one patient with an irregular heart rhythm on land, which becomes regular during immersion. In addition, stroke volume improved and heart rate decreased. 3A. On land, LVOT VTI 13.6 cm, stroke volume 57 mL, heart rate 74 bpm, cardiac output 4.2 L/min. 3B. During warm water immersion, LVOT VTI 20.9 cm, stroke volume 88 mL, heart rate 58 bpm, cardiac output 5.1 L/min. LVOT: left ventricular outflow tract, VTI: velocity time integral.