First Minister Rhodri Morgan is expected to stay in hospital for the next couple of days after treatment for two blocked arteries.
Rhodri Morgan is 'in good spirits' after his procedure
Mr Morgan, 67, was admitted on Sunday evening after feeling unwell and a subsequent angiogram showed two partially-blocked arteries.
Two "stents" were inserted in a "standard surgical procedure" and Mr Morgan was conscious throughout.
Talks about a coalition cabinet, which were due to take place, were delayed.
Mr Morgan had been reported to be suffering from gastric problems.
His wife, Julie, the Cardiff North MP, said he had reported being in "terrible pain and alarmed", which he attributed to eating chillies.
Mr Morgan spent the night in Llandough Hospital in Penarth but later on Monday was transferred to the University Hospital of Wales in Cardiff for the angiogram, which revealed the two partially blocked arteries.
A statement from Jane Hutt, minister for budget and business management, read: "The first minister felt unwell yesterday afternoon and was taken to Llandough Hospital where he remained overnight for tests.
"Doctors decided as a further precaution that he should undergo an angiogram.
"The angiogram showed that two arteries were partially blocked, and two stents were inserted. This is a standard surgical procedure.
Returning to work
"The first minister was conscious throughout and is in good spirits."
Dr Clive Weston, consultant cardiologist at Singleton Hospital in Swansea, told BBC Wales that the insertion of two stents should allow Mr Morgan to return to very good health.
However, he also warned that the need for the procedure was a clear suggestion that Mr Morgan was a candidate for a heart attack.
He thought that his condition was likely to have been aggravated by stress, and that Mr Morgan may now need to reassess his lifestyle.
Asked how soon the First Minister might return to work, he said that in general, a patient would need to wait a few weeks before returning to work.
Dr Liam Penny, a consultant cardiologist at the University Hospital of Wales, told BBC Wales the stent surgery was a "routine procedure".
'Robust and resilient'
"We did over 1,000 cases last year at the Heath hospital, and it's a very effective treatment for angina," he added.
On Monday, Mr Morgan and Plaid leader Ieuan Wyn Jones were due to discuss how many cabinet seats - and which posts - Plaid will fill after both parties voted for a coalition deal at the weekend.
Mr Jones said he wished Mr Morgan well and a speedy recovery.
He said he looked forward to the First Minister returning to work and completing their discussions.
Welsh secretary Peter Hain said: "Rhodri is a remarkably robust and resilient person and I'm sure he will bounce back to full public life sooner rather than later.
"I have also spoken to Jane Hutt this evening and told he we will work closely together to assist her in anyway through this period."
On Friday, Labour members approved by a 4-1 margin the One Wales document Mr Morgan had agreed with Plaid, although many Labour MPs and some AMs are strongly opposed.
On Saturday, Plaid's national council also backed it, but by an even bigger margin, with 92% in favour.
The assembly is due to go into recess later this week.