[Your letterhead, if desired; if not, your return address]
[Date of letter-month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
I am so very sorry to hear the sad, sad news about the loss of your beloved cat, Fluffy. I know how much Fluffy has suffered with various illnesses over the past couple of years and how caring you have been to meet her every need. I was really hoping that she would have been able to recover. You and Fluffy have shared so many special times over the past 14 years, and I know you will treasure those memories in your heart.
Of course, you must be suffering so terribly over this loss. Please let me know if there is anything I can do to help, and I trust it helps at least a little to know that I and many others care deeply about you and want to comfort you at this time. I will talk with you soon-I'll call to check on you in a day or two-and in the meantime am sending much love your way.
[Sender's first and last names]