Bhakti is there in the heart but is covered. By using the senses to serve Kṛṣṇa the senses become purified as well as the mind and the other coverings of the soul. In this way our bhakti becomes more revealed.
Even if you have some material desires mixed with bhakti… that is still bhakti just not at the highest level. If you still have some material desires, you need to practice sādhana–bhakti. Sādhana–bhakti will be discussed further below.