Ensign, R-Nev., now in his second term, announced March 8 he will not be running for a third. During his second term, he had an affair with the wife of one of his aides, and the couple received a large payment from his parents.
Heller touted his opposition to "reckless government spending" in his e-mail, The Hill reported.
A former stockbroker, Heller served in the Nevada Legislature and was state treasurer before his successful run for Congress in 2006.
"As families across Nevada struggle to pay their bills and fight to keep their homes, Barack Obama and his beltway allies are proposing record spending that will add to America's job-killing debt from a stratospheric $14 trillion to a staggering $20 trillion," he wrote.
A recent Public Policy Polling survey showed Heller leading likely Democratic candidates. Rep. Shelley Berkley, D-Nev., is considered a possible pick but has said she has not yet made a decision.