Hooker Kirby Myhill scored two tries with Josh Turnbull, Seb Davies, Blaine Scully, Willis Halaholo and Alex Cuthbert additionally crossing the whitewash for the Welsh area.
Cardiff fly-half Jarrod Evans kicked 5 conversions within the 45-12 victory.
The Kings, backside of Convention B, scored twice, with tries for stand-off Ntabeni Dukisa and Lindokuhle Welemu, with Masixole Banda slotting one conversion.
The victory for the Blues adopted Ospreys’ defeat to Ulster which meant any win over the South African facet would have been ok to safe a top-four end.
Danny Wilson’s facet led 33-Zero on the break after tries from Cuthbert, Davies, Turnbull, Halaholo and Myhill.
Dukisa scored a comfort within the second half however the Kings defence remained leaky as Myhill touched down for a second and Scully additionally crossed the road.
The match fizzled out within the final quarter as Welemu scored one other attempt for the hosts, however it was not sufficient to show the tide in opposition to Cardiff.