Why did Iran suffer from international sanctions?

Iran’s President designed a five-day tour of Latin America, something the US officials described as a sign of desperation as Iran copes with heavy international sanctions placed on Tehran after its refusal to halt its nuclear program. President Mahmoud Ahmadinejad’s first stop is Venezuela, he then visits Nicaragua, Cuba and Ecuador. Iranian state media quoted the President as praising the revolutionary spirit of the leaders of those four nations. Ahmadinejad has recently courted leftist Latin American leaders including Venezuelan President Hugo Chavez, a long time critic of the US. On Friday, the US officials urged Latin American countries not to deepen their ties with Iran.
                                                                VOA 2012-1-09