Cab-sauv or cabernet sauvignon is from a single grape variety and is not a blend. One of the greatest red varietal wines in existence for big full bodied to elegant wines if the right source grapes are used.

Cabernet Sauvignon Blends are often made with other varities such as Shiraz. Others might blend with Merlot or Malbec, perhaps with Shiraz as well. Both Merlot and Malbec will make a "softer" wine.

Sometimes a straight varietal Cabernet Sauvignon will actually have up to 10% of another varitey to get the "right" result in the bottle. A "straight" varietal with less than 15% of other varieties need not detail the other varieties on the label (ie 85% or more = one variety) per most countries labelling requirements.

A good example of the above is the Australian wine "Grange" which is labelled as Shiraz. But it may actually contain around 10% of Cabernet Sauvignon (the percentage might vary from 0% to less than 15%) depending on what the winemaker is trying to achieve.