The Kremlin said on Thursday that Russia is granting Venezuela a $1bn loan for the purchase of Russian weaponry.
A Russian naval squadron is also on its way to Venezuela, and Russia sent two strategic bombers there earlier this month.
Medvedev told Chavez: "This (the upcoming naval drill in the Caribbean) shows the strategic framework of our relations. I am sure that your visit will be successful.
"We will talk about the situation in the world, in Latin America and Europe, especially taking into account the Caucasian crisis... We appreciate the moral support of Venezuela in this situation."
The arms purchases have sparked concern in the US and among some of Venezuela's neighbours, including Colombia which has accused Venezuelan officials of supporting left-wing armed groups.
Heads of Venezuela's state oil company Petroleos de Venezuela (PDVSA) and Russia's state gas monopoly OAO Gazprom signed a memorandum of understanding that Gazprom said allowed for greater co-operation between the companies.
The energy ministers signed a separate memorandum calling for the establishment of a body that would oversee broader co-operation in oil and gas between the energy-rich nations.
Gazprom has invested $100m in Venezuela, Alexei Miller, the Gazprom chief, said on Russian television after the signing.
He said an agreement to create a consortium linking PDVSA with Russia's top oil and gas companies was in the works and could be signed in the coming months, with Gazprom likely to lead the Russian side.
Chavez is on a trip that has already taken him to Cuba and China along with Russia, whose war with Georgia has damaged relations with the US.
The western hemisphere naval deployments are a pointed response to the US use of military ships to bring aid to Georgia, and aspects of what the Kremlin casts as threatening US encroachment near its borders.
Chavez thanked his "friend" Medvedev on Friday and reiterated his backing for Russia's actions in the Russia-Georgia war.
"I would like to use this occasion to offer our full, modest but completely solid support for Russia's actions" in the Caucasus, said Chavez, adding: "We understand how the people of South Ossetia were attacked."