Possible Clues:

• What's there is not in vain, by the sound of it
• It carries blood from the left ventricle
• Trunk feature
• (evens favourite) A Main Vessel
• A bloody vessel or thanks
• A main arterial road
• Coronary artery adjunct
• Biggie in circulation?
• Major outlet
• '69 self-titled debut from psychedelic Chicagoans