Hi; this is a fun one because though both Iraq and Syria were both ruled by members who claim(ed) to be part of the Ba'athist party, neither nation recognized the legitimacy of the other through most of the 1970's and 1980's.

See, both groups of Ba'athists (which means "Renaissance" in Arabic) were extremely hostile towards each other, with the very short-lived exception of the 1973 Yom Kippur War. During the 73 war, Iraqi president al-Bakr temporarily patched things up between the two countries because of the shared goal of attacking and beating the Israelis. Iraqi military units tried to bolster the Syrian army as the Syrians tried to exploit the surprise attack and change in tactics by Egypt; a change which flustered the Israelis and might have given the Arab armies a chance against the usually technologically- and strategically-superior foe. Syria, however, was not militarily ready to capitalize upon Israeli uncertainty in any meaningful way.

Unfortunately (or depending upon your perspective, fortunately) relations got even worse after the UN-brokered cease-fire; Syria accepted but Iraq didn't. Hafez al-Assad (president of Syria) and Saddam Hussein (Assisstant Secretary of the Iraqi Ba'athist Party) were definitely antipathetic towards each other; Hafez called Saddam Hussein a 'dirty Tikriti bandit' and Saddam called Hafez a coward for Syria's quick acceptance of the UN deal. Still, there were a couple of attempts by al-Assad to smooth things over in the mid-1970's, mostly to no avail.

It was probably this hatred which partially led to the coup in Iraq which vaulted Hussein from Deputy Secretary to President; Hafez had proposed a union of sorts between the Syrian government and the Iraqi government in the late 1970's [similar to the short-lived unity between Egypt and Syria in the 1960's] and Hussein probably would have been on the outs had it been successful. Hussein forced al-Bakr to 'retire' and then took over the reins of Iraq for himself.

Probably the worst the relations between the two have been was in the 1980's, culminating in 1990 when Syria joined an anti-Iraqi coalition of Arab states following the invasion of Kuwait. Prior to that, Syria had tiffs with its neighbor over the border, the flow of illegal smuggling, and even the water from the Euphrates. Saddam - busy jumping at shadows from the Iran-Iraq war - even accused the Syrians of plotting to kill him (though he did claim this plot pretty much from day 1 of his 'presidency,' so it was probably a familiar tune).

There's an older book by E. Kienle Ba'ath versus Ba'ath: The Conflict Between Syria and Iraq 1968 - 89 that goes into more detail about it. Hope that helps!