In 1969 Maessen and her older sisters Patricia and Bianca formed a group, calling themselves Hearts of Soul. Following several single releases, and a No. 11 chart hit with "Fat Jack", they took part in the 1970 Dutch Eurovision selection, where their song "Waterman" ("Aquarius") earned a narrow victory, qualifying them for the 15th Eurovision Song Contest, which took place on 21 March on home ground in Amsterdam. Technically, groups of more than two singers were still barred from Eurovision at that time, so to get around this they billed themselves as 'Patricia and the Hearts of Soul', implying that Stella and Bianca were backing singers to Patricia's lead. In a small field of 12, "Waterman" placed seventh.