Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 23

Sanskrit:

श्रीशुक उवाचएवमुक्त्वा स देवर्षिर्गतो नारायणाश्रमम् ।नलकूवरमणिग्रीवावासतुर्यमलार्जुनौ ॥ २३ ॥

ITRANS:

śrī-śuka uvācaevam uktvā sa devarṣirgato nārāyaṇāśramamnalakūvara-maṇigrīvāvāsatur yamalārjunau

Translation:

Śukadeva Gosvāmī continued: Having thus spoken, the great saint Devarṣi Nārada returned to his āśrama, known as Nārāyaṇa-āśrama, and Nalakūvara and Maṇigrīva became twin arjuna trees.

Purport:

Arjuna trees are still found in many forests, and their skin is used by cardiologists to prepare medicine for heart trouble. This means that even though they are trees, they are disturbed when skinned for medical science.