Chavez's latest world tour is taking him to several countries whose governments are eager to limit the influence of the US.
He trip to Russia followed talks in China, with Hu Jintao, the country's president.
According to Russian media reports, Venezuela has been asking for an arms loan for months.
Russia's Kommersant daily newspaper reported on Thursday that the visit was part of the run-up to local elections in Venezuela and that the leftist leader would use the trip to stress his alliance with Russia against the United States.
Chavez and Medvedev may observe Russian army exercises taking place in Orenburg, Kommersant reported, an event that would emphasise the growing military ties and arms sales between the two countries.
In deployments not seen since the Cold War, Russia this month sent two long-range bombers to Venezuela for exercises and has dispatched a flotilla of warships from the Arctic base of Severomorsk to Venezuela near US waters.
Venezuela has bought Russian fighter jets, tanks and assault rifles and is planning to purchase anti-aircraft systems, armoured personnel carriers and more combat aircraft, Kommersant reported earlier, quoting Russian officials.
During his visit to Russia, Chavez is also reportedly expected to make a statement supporting Russian military action against Georgia last month.
US-Russia relations are at one of their lowest points since the end of the Cold War because of tensions over Russia's conflict with Georgia and US plans to site missile defence facilities near Russia's borders.
Venezuela, which is to hold local elections in November, expelled the US ambassador to Caracas earlier this month in what Chavez said was an act of solidarity with Bolivia which also expelled its US envoy.
After his visit to Russia, Chavez is due to visit France and Portugal as part of an international tour that has already taken him to China and Cuba.
Meanwhile, Medvedev said on Thursday that Russia's plans to modernise its armed forces will not be affected by the global financial crisis.
"Regardless of any crisis we should build new submarines, should simply deal with the modernisation of the armed forces," Medvedev told the crew of St George the Victor nuclear submarine during a visit to its Pacific home base at Kamchatka Peninsula.
"Our country has means and resources for that," he said in comments showed on national television.
Putin made the revival of the armed forces, neglected in the first post-Soviet decade, a symbol of Russia's resurgence and an additional argument in Moscow's foreign policy.
Medvedev has said the recent war in Georgia showed Russia needed to equip its army with more advanced weaponry and Putin has said the military budget will grow by 28 per cent next year.