LAS VEGAS - Marvin "Sweet Louie" Smith, one half of the R&B duo, the Checkmates, has died. He was 68.

Smith died Saturday of a heart attack aboard the Caribbean Princess cruise ship in the Caribbean, where he was scheduled to perform, said his agent, Mike Moloney. Smith's counterpart, Sonny Charles, a friend since childhood in Fort Wayne, Ind., found Smith in his cabin, Moloney said.

The duo's best-known recordings include "Love is All I Have to Give" and a remake of "Proud Mary." But 1969's Phil Spector-produced "Black Pearl" was their most successful, a Top 10 hit.

The duo's highlights included performing with Frank Sinatra at Oakland Coliseum, a concert at Madison Square Garden with Herb Alpert and singing the national anthem for the "Thrilla in Manila," the Muhammad Ali-Joe Frazier championship boxing match in the Philippines. *