Steinman died Monday in Connecticut, according to the state's medical examiner. The cause of death is unclear. We do know it appears it was sudden ... there was a medical emergency call to his home around 3:30 AM Sunday to transport a male patient.

Jim's perhaps best known for his songwriting work on Meat Loaf’s "Bat Out of Hell" -- one of the best selling albums of all time -- and "Bat Out of Hell II: Back into Hell" ... writing and producing the smash hit, "I'd Do Anything For Love (But I Won't Do That)."

Steinman's got his fingerprints all over Bonnie Tyler's albums, writing and producing her biggest hit, "Total Eclipse of the Heart."

Jim also wrote and composed Air Supply's "Making Love Out of Nothing at All" and Barry Manilow's "Read 'Em and Weep," which was originally written for Meat Loaf.

He's also the brainchild behind another power ballad, "It's All Coming Back To Me Now," first recorded by Pandora's Box and then made famous with Celine Dion's cover.

Jim also worked with Def Leppard, Barbra Streisand, Billy Squier and The Sisters of Mercy. You wanna talk about accomplishments ... for 3 straight weeks in 1983, Jim was responsible for the #1 and #2 songs on Billboard -- 'Total Eclipse' was in the top spot, and 'Making Love' was second.

Steinman was 73.