Altitude Sickness in the Qur'an Only one Qur'anic verse alludes to the physiological effects of ascending in "the sky." The Qur'anic key words and concepts include: heart, bosom; ascending; sky; punishment; restricted, narrow, hence difficult; constricted, straitened, hence troubled; the people who seek admonition or remembrance from God's signs. Allah said, "So whomsoever God wills to guide, his bosom He opens wide towards Islam (lit, the surrender); and whomsoever He wills to let go astray, his bosom He causes to be restricted and constricted as if he were ascending in the sky. It is thus that God inflicts punishment on those who do not believe. And this, thy Sustainer's way, is straight. Clearly, indeed, have We spelled out the signs for people who take admonition!" (Qur'an 6:125-126) There are many verses in the Qur'an where the heart and the bosom or chest are referred to in the physical and metaphorical senses. In this verse, the bosom is mentioned twice but with two different meanings. Here we are concerned with only the physical effects of ascending in "the sky." The heart develops problems as if it was getting closed and constricted. The questions we may raise are: Does ascending in the sky mean both going up to higher altitudes as in mountain climbing, and ascending into upper atmospheric regions and space? Are the conditions described in the verse correct according to our modern sciences and experience? What causes the effects described in the two adjectives, and how can we interpret them? What kinds of problems, or punishments, can be expected from such ascending? What are God's "signs" or laws concerning such ascending in relation to human physiology? Who are the "believers," and the people who remember or take admonition from these signs of God? Effects of Ascending to Higher Altitudes on the Heart The earth's atmosphere is an "ocean" of air which gets thinner as we rise up. Over 99% of the atmosphere lies below the thermosphere - the layer that begins about 50 miles above the earth. With less air, air pressure decreases with altitude. It is 14.7lbs. per square inch at sea level, 10.2 at 10,000 feet elevation, 6.4 at 20,000 feet, and only 1.6 lbs per inch at 50,000 feet (about 9.5 miles) altitude. Man needs oxygen and air pressure to survive. Most people are accustomed to living under 5,000 feet. The Tibetans and Indians of Bolivia have adapted to high altitudes up to 17,000 feet; they do hard labor, though newcomers may pant for breath at each step. The amount of oxygen entering the blood stream decreases at higher altitudes because of reduced atmospheric pressure. If the oxygen content of the blood drops below the body's needs, one gets "altitude sickness." This is characterized by shortness of breath, fatigue, headache, dizziness, nausea, and faulty judgement. Anoxia is the lack of a normal supply of oxygen to body tissues, or their failure to utilize oxygen. Anoxic anoxia occurs when blood flowing in the lungs does not take in enough oxygen due to lack of oxygen in the air breathed, or diseases of the lungs and blood. This scarcity of oxygen occurs at 10,000 to 15,000 feet (altitude), in poorly ventilated areas, etc. Healthy people develop symptoms of anoxic anoxia when they breathe air with two-thirds or less the normal oxygen content. They may lose consciousness when they get one-half or less of needed oxygen, but life may be saved if oxygen is given immediately. Conclusions Prophet Muhammad and the people in Arabia, could not know or anticipate the conditions and problems of even mountain climbing. Almost none of the world's famous peaks were climbed until the 1800s. The Arabian peninsula, even Africa and West Asia, do not have the higher mountains of the world. However, the pre-Qur'anic literatures of the East and the West gave prominence to mountains and the sky in their epics and myths. These were the "mythical places" of their gods, goddesses, demons, and dead souls. By contrast, Qur'anic references to ascending the sky are associated with knowable laws and experiences of physiology and the atmospheric sciences. The Qur'anic verse points out the hazards of ascending in the sky. It describes the symptoms associated with the reduction of air, oxygen and atmospheric pressure, and the effect on the function of the heart which slows down and stops with the diminishing supply of oxygen in the blood. The "believers" and "people who mind or take admonition" are those who understand the 'signs" of God concerning the body's need for oxygen, the natural or man-made conditions of scarcity of oxygen at higher altitudes, and take measures to prevent and avoid the "punishment" for violation of God's laws. For example, they provide a supply of oxygen when they travel in the air or space, go mountaineering, work in mines, etc.