Originally Posted by truthseeker63
Officially yes and almost certainly privately too. But his actions suggest he was willing to adapt his beliefs around his duties as head of state and the necessities of unity.
Throughout his life he was actively involved in religious affairs and was a pioneer of linking religion with the state to act as a unifying force. His amazing victory over the Persians - one of the greatest military comebacks of all time and unjustly forgotten - was defined in religious terms. However, the very act of trying to unify the state under a single creed caused him to come into conflict both with other religions within the state (eg Judaism) and in particular Monophysite Christians. His attempted compromise (Monothelitism) ultimately failed and led to even more confusion. These schisms contributed to the success of the Muslim military expansion.
There is an account which is widely reported in Muslim circles (Bukhari and others) of a conversation in Jerusalem between Heraclius and Abu Sufyan, a Muslim merchant. According to this Heraclius was persuaded that Muhammad was the true prophet and wanted to convert, but his people wouldn't let him.
However, there is no historical reference to this idea and nothing in Heraclius's known behaviour to indicate that it's true. For instance, just a short time after the alleged meeting he went to great lengths to recover the True Cross from Persian hands and made a great display of it. When war began between the Muslims and the Byzantines he fought to defend his ground energetically with no sign of any Muslim leanings. Based on events, it's difficult to see how it could be true and was probably written later.
However, it has led to many Muslims retaining a favourable attitude to Heraclius.