Last Woman on Earth

Harold Gern, a successful businessman from New York who is constantly in legal trouble, is spending a holiday in Puerto Rico with his attractive wife Evelyn, whom he married “between trials”. They are joined by Martin Joyce, Harold's lawyer, who has come to discuss the latest indictment. Harold invites him along on a boat trip during which all three try out some newly bought scuba diving equipment. When they resurface, they are unable to breathe without using their scuba tanks. They climb back into their boat and find Manuel, the crewman, dead, apparently of asphyxiation. Upon rowing ashore, they enter the jungle. (from Wikipedia)