Protect cardiovascular system. The ice hole at the entrance of the Russian sauna is mainly to protect the human body's cardiovascular system. The details are as follows: The ice hole at the door of the Russian sauna has the most significant impact on cardiovascular health. When the human body enters a high-temperature environment, blood vessels will expand, blood pressure will decrease, and heartbeat will accelerate. This process is called the "warm-up response." When the human body enters a low-temperature environment, blood vessels will constrict, causing blood pressure to rise and heartbeat to slow down. This is called a stress response. The ice cave at the door of the Russian sauna can promote vasoconstriction and increase blood pressure, thereby exercising the cardiovascular system. It can enhance myocardial contraction, reduce cardiac load, improve cardiovascular function, and reduce the risk of heart disease.