Cavendish, 25, becomes the first British rider to lead the Vuelta a Espana since Robert Millar in 1986.
Mosquera finished second behind Italian Vincenzo Nibali in La Vuelta earlier this month.
The 21-stage 65th edition of the Vuelta ends in Madrid on 19 September.
Heras' biggest win to date is the Vuelta (Tour of Spain), in which he has triumphed three times, including last year.
Ezequiel Mosquera and his Xacobeo team-mate David Garcia Da Pena both tested positive for banned substance hydroxyethyl starch during the Vuelta.
The 21-stage 65th edition of the Vuelta, in which 198 riders from 22 teams are competing, ends in Madrid on 19 September.
"Por la Vuelta" comes from Santaolalla's aptly titled recording, Ronroco.
The Kazakhstan native was one of the favorites to win this year's Tour de France after a breakthrough performance that won him first place in the 2006 Vuelta a Espana.
Estoy muy feliz de estar de vuelta a clases.
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"Lo tenemos a la vuelta de la esquina", dijo.
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Cavendish, 25, is making his debut in the Vuelta a Espana but is joined by only one of the HTC-Columbia line-up that helped him win five stages of the Tour de France in July - Austrian Bernhard Eisel.
Uno de los principales candidatos es el ex presidente Akbar Hashemi Rafsanjani, el favorito en los sondeos, pero es posible que no consiga suficientes votos para ganar en la primera ronda de votaciones y tenga que enfrentar una segunda vuelta electoral.
The 34-year-old knows the terrain well around Varese but will have to fend off the challenge of Oscar Freire and his powerful Spanish squad, which includes Vuelta Espana winner Alberto Contador, Olympic champion Samuel Sanchez and UCI ProTour winner Alejandro Valverde.
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