Updated 12 October: Thanks to the suggestions below, I’ve now added the following text to Teide information in the Essentials and Resources tabs.
Teide is a staggering 3,718m high, making it the highest point in Spain and the third highest volcano in the world. The caldera, and indeed the national park generally, has an average altitude of over 2,000m. Please note that atmospheric changes start at an altitude of around 2,500m. This can cause altitude sickness, but more specifically, can cause problems for those suffering heart and lung conditions, who can also begin to suffer repercussions at lower altitudes. Such people are advised not to go above the level of the caldera, and so should not go up in the cable car, nor to try to ascend the peak of Teide itself. Those with severe heart or lung conditions would be well advised not actually to go even as high as the caldera itself.
Original post 6 October: A 62-year-old British man died this lunchtime after suffering a heart attack in the Teide National Park. The poor man was taken ill at the Roques de García opposite the Parador around 12.20, and emergency services were called with reports that he was unconscious after falling. Paramedics were dispatched by helicopter and attempted to resuscitate him, but despite prolonged efforts, they were unable to bring him around and he was declared dead at the scene.