Take a look at the American Enterprise Institute's interactive map of "Global Business in Iran": <www.aei.org/IranInteractive/>. Impressions that many have to the contrary, Russian business transactions with Iran are apparently in the same league as those of Canadian and American businesses. Russia's interests in Iran are more geopolitical than economic.
After looking at the map, click on "Analysis," and then click on "Bilateral Trade Ranking, by $ Amount of Business Transactions, 2000-Present." The main business partners with Iran are China (44.45% of the total)* and India (34.97% of the total), which are way ahead of France, Germany, and Italy.
If the AEI's research is accurate, whether Iran can survive economic sanctions depends a lot on China and India.
* See, also, Paulo Prada and Betsy McKay, "Trading Outcry Intensifies: Firms Face More Calls to Cut Ties With Censured Nations," Wall Street Journal 27 March 2007.