Hannah Wynne Richards, 63, was found dead in the office above her premises in Sketty, Swansea, on 20 January by a nurse who worked with her.
She had taken a cocktail of drugs from her surgery.
Coroner Colin Phillips said Ms Richards had been "facing financial pressure".
He ruled her death was suicide.
Swansea Coroner's Court heard three letters were found next to Ms Richards' body -  one to the coroner and the others containing money for Jeanette Hunt, who discovered her body, and a woman who looked after her horses.
The one addressed to HM Coroner read: "You are probably returning a verdict of suicide, murder by Inland Revenue would be more accurate."
The letter to Ms Hunt said how loyal her employee had been and explained that she could not pay her tax or livery fees.
It also contained Â£290, thought to be for wages, the inquest heard.
Mr Phillips said Ms Richards had been "facing financial pressure" at the time of her death and added: "She was not a business person and she placed the needs of her animals before her own personal interests."
The inquest was told Ms Richards, who set up Penybryn Veterinary Centre in 2007, had no relatives living near her and had little interaction with people outside her working life.
Instead, she devoted herself to caring for animals - at the time of her death she was living in a basement flat behind the surgery but was known to sleep in the office when she was looking after animals.
PC Jason Sullivan said: "She was regarded as an extremely gifted and caring vet who would do all she could to save an animal's life."
The inquest was told that Ms Richards did not have a "good business head" and always said the welfare of the animals was paramount.
A post-mortem examination found Ms Richards' cause of death to be multiple drug toxicity and listed four drugs used in veterinary work, which were found in her system.

He had been out of work since parting company with the Robins in November.
Crawley, who were relegated from League One earlier this month, had been without a manager since John Gregory left the West Sussex club on 9 May.
"My job is to put a competitive squad together that will challenge at the right end of the table," 45-year-old Yates told the Crawley website.
He spent almost five years in charge of Cheltenham and guided them to the League Two play-offs in 2012 and 2013.
After successive top-seven finishes and unsuccessful play-off campaigns, Cheltenham finished 17th in League Two in 2013-14.
And ex-Kidderminster boss Yates was then sacked late last year, following a run of four successive league defeats that left them 18th.
He was the third-longest serving manager in England's top four divisions at the time of his departure from Whaddon Road.
"I have been out of the game for a few months and when this opportunity came up it really excited me," he said.
"There's a big challenge ahead but one I am really looking forward to."
Gregory, 60, parted company with Crawley earlier this month, having spent the past six months recuperating from heart surgery.
Dean Saunders was placed in interim charge of the Reds in December, but was unable to save the club from the drop to League Two.
The 50-year-old former Liverpool and Aston Villa striker was appointed Chesterfield manager last week.
Crawley chief executive Michael Dunford said that Yates stood out among "some very strong candidates".
He added: "He has a very deep knowledge of the level we find ourselves at next season and is a first-rate coach.
"The board spoke to several people in the game who have worked with Mark and they were all very positive about his credentials, his knowledge and his enthusiasm."
A vet who killed herself left a note to the coroner saying a conclusion of "murder by Inland Revenue" would be more appropriate than suicide, an inquest has heard.
[NEXT_CONCEPT]
Crawley Town have appointed former Cheltenham boss Mark Yates as their new manager on a two-year deal.