Cristerna, 48, was previously head of M&A for Europe, Middle East and Africa, while Ventresca, 46, was head of M&A for North America.
They will report to Jeff Urwin, global head of investment banking.
A spokeswoman for the bank confirmed the contents of the memo.
JP Morgan ranks second behind Bank of America Merrill Lynch on worldwide M&A advisory with $161.5bn (£105.4bn) of announced deals since the beginning of the year according to Thomson Reuters data.
Most recently, Ventresca led Virgin Media’s Liberty Global deal, as well as United Technologies $16.5bn acquisition of Goodrich, Dollar Thrifty’s sale to Hertz for $1.2bn and Ingersoll Rand’s announced spin-off of its security business.
Cristerna has worked on numerous sizeable cross-border transactions, including DE Master Blenders’ $9.8bn spin-off from Sara Lee, the merger of Iberia and British Airways and Inbev’s acquisition of Anheuser Busch for $52bn in 2008.