Iran's currency, the rial, has lost "considerable value" and there have been "runs on the bank" as Iranians try to dump domestic currency and acquire assets that will hold value better as inflation "takes off," Petraeus said.
Director of National Intelligence James Clapper acknowledged that sanctions so far had not caused Iran's leaders to change their pursuit of nuclear capabilities.
But he said some Iranian officials appear more willing to conduct an attack in the United States if they feel threatened, citing last year's alleged Iranian plot to kill the Saudi ambassador to Washington.
"The 2011 plot to assassinate the Saudi ambassador to the United States shows that some Iranian officials - probably including Supreme Leader Ali Khamenei - have changed their calculus and are now more willing to conduct an attack in the United States in response to real or perceived U.S. actions that threaten the regime," Clapper said in his Senate testimony.
"We are also concerned about Iranian plotting against U.S. or allied interests overseas," he said.
Senators at the hearing asked about Israel's concerns about Iran's nuclear program, amid speculation that Israel might launch a pre-emptive strike at the country's known nuclear sites.
Senator Dianne Feinstein, the panel's chairwoman, and Petraeus said they met recently with the director of Mossad, Israel's intelligence service.
"We're doing a lot with the Israelis, working together with them. And of course for them, this is, as they have characterized, is an existential threat," Clapper said.
Petraeus, appearing with other intelligence community leaders at an annual open hearing on global threats to U.S. security, said that China has reduced imports of Iranian oil but "it remains to be seen whether that continues."
"It appears that Saudi Arabian production is ramping up and can fill some of the demand that might have been met by Iranian exports now that there are the sanctions on the Central Bank of Iran," he said.
The United States imposed the harshest sanctions so far on Iran when President Barack Obama on December 31 signed into law new sanctions on transactions involving Iran's central bank.
The European Union last week imposed a ban on the import, purchase or transport of Iranian oil. Existing contracts can be honored up to July 1.
The West has imposed sanctions over the years due to concerns that Iran's nuclear development program is aimed at building a weapon. Iran says its program is for peaceful purposes.
The latest U.S. sanctions will have a deeper impact because the Central Bank of Iran handles a large volume of foreign bank transactions and receives the revenue for the roughly 70 percent of oil sold by the National Iranian Oil Company, Clapper said.