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.
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.