Envision Healthcare Holdings Inc. and AmSurg Corp. agreed to merge in an all-stock deal that will create a super-sized US provider of physicians and healthcare services with a combined enterprise value of $15 billion, Bloomberg reports. The transaction will create one of the largest US providers of physicians in specialties, including emergency, anesthesia, radiology and children’s services. AmSurg last year dropped its bid for Team Health Holdings Inc. (NYSE: TMH) after the target company rejected merger offers.