What does normal systolic and low diastolic blood pressure mean?

Valve issue: It can be a sign of a specific type of heart valve condition. I recommend seeing a cardiologist for an evaluation.

Nothing: In health, your body lowers your diastolic pressure to whatever is required to maintain proper perfusion of blood to your entire body. There's really no such thing as 'low diastic pressure' in my opinion, and I've never seen in four decades in medicine anything to make me think this is something you should worry about.