Had not the doctor arrive in time,he would have died of hear

这是虚拟语气的倒装句型,
原句应为if the doctor had not arrived in time,he would have died of heart attack.是对过去某个事实的虚拟语气,因为实际上医生及时赶到了.
句型结构是 if A had not done sth,B would have done sth.
表示如果不是A做了某事,B可能已经怎么这么了.具体到本句就是要不是医生及时赶到,他可能已经死于心脏病了.