even though [someone] is busy忙しいのに combines 忙しい (busy) with のに (even though; despite). The subject is often understood from context. It can also be used with past tense, as in 忙しかったのに (even though [someone] was busy).
JA: 忙しいのに手伝ってくれてありがとう。
EN: Thank you for helping me even though you’re busy.