SB 12.3.49

tasmāt sarvātmanā rājan
 hṛdi-sthaṁ kuru keśavam
mriyamāṇo hy avahitas
 tato yāsi parāṁ gatim
Synonyms: 
tasmāt — therefore; sarva-ātmanā — with all endeavor; rājan — O King; hṛdi-stham — within your heart; kuru — make; keśavam — Lord Keśava; mriyamāṇaḥ — dying; hi — indeed; avahitaḥ — concentrated; tataḥ — then; yāsi — you will go; parām — to the supreme; gatim — destination.
Translation: 
Therefore, O King, endeavor with all your might to fix the Supreme Lord Keśava within your heart. Maintain this concentration upon the Lord, and at the time of death you will certainly attain the supreme destination.
Purport: 

Although the Supreme Lord is always in the heart of every living being, the words hṛdi-sthaṁ kuru keśavam indicate that one should endeavor to realize the Lord’s presence there and maintain this awareness at every moment. Parīkṣit Mahārāja is about to give up this world and is receiving final instructions from his spiritual master, Śukadeva Gosvāmī. In the context of the King’s imminent departure, this verse has special significance.