Panama is organizing the April summit, which has brought together leaders at three- to four-year intervals since 1994 at different locations around the region.
Panamanian Foreign Minister Isabel de Saint Malo said Cuba and several other countries had confirmed they would attend the summit within days of receiving a formal invitation.
It was unclear whether Havana would be represented by Cuban President Raul Castro, or someone else.
"Panama is working for all the heads of state and government from the 35 countries of the Americas to be present at the VII Summit," Saint Malo said in an email to international news agencies.
More From This Section
The United States, which hosted the first summit in Miami, has long been reluctant to include Cuba, one of the last of its Cold War adversaries and still the target of a half-century-old trade embargo.
"Even given the region's heterogeneity, more issues unite us than divide us and these are the ones we will concentrate on," said Saint Malo.
Saint Malo was in Miami this week for a conference on Latin America organized by former US president Bill Clinton.
Chile, Colombia, Mexico, Guatemala, Costa Rica and El Salvador have also said they will attend, she said.