What is Kounis syndrome, which caused Sunjay Kapur's death?

Indian industrialist Sunjay Kapur died suddenly during a polo match in England on 12 June, with doctors now attributing cause to Kounis syndrome – a rare condition in which an allergic reaction, triggered in his case by a bee sting to the throat, led to a fatal heart attack. The often underdiagnosed syndrome can be deadly without rapid, targeted treatment.