I'm doing Rippetoes as it is defined. Monday...Wednesday...Friday

On the off days I am doing HIIT training. 15 minute maximum on HIIT training.

Is this enough activity to get big AND keep my heart in good condition? I know that I can get big with the rippetoe routine...I am already seeing good gains. But what about my heart and cardio system...will they benefit from doing this as I am doing it?