Chronic heart problems are the top underlying health factor in Covid-19 patients ending up in intensive care.
People with respiratory disease, diabetes and obesity also made up a high proportion of those in ICU as another 37 deaths were announced.
The death toll from Covid-19 has climbed to 1,375 and there have been a further 265 new cases.
Of 327 patients admitted to ICU, 165 suffered from chronic heart problems, 76 from respiratory illness and 74 from diabetes.
There were 53 intensive care patients with a body mass index of greater than 40, while others were admitted to ICU with asthma, cancer and renal issues.
Some patients had more than one of the conditions.
Chief Medical Officer Dr Tony Holohan said he was “hopeful” the country remains on track to launch phase one of easing restrictions on May 18.
He added: “We have seen continued improvement. We are seeing a persistent number of infections coming from the community, particularly from younger people in the community.
“It is a number that isn’t falling as much as we would like. We are keeping an eye on that.
“I won’t sit here today and say that we are going to be in the position on May 18. If conditions were today we still aren’t at that point but I am hopeful.”
There have now been 22,248 people infected with coronavirus including 2,878 who had to be taken to hospital.
New data shows that 17,110 patients have recovered from the bug – a rate of 78%.
Testing capacity is on track to hit its 100,000 per week target by May 18.
However, more work is needed to ensure the turnaround time in results is fast enough to catch new outbreaks of the virus when lockdown ends.
Dr Holohan said the HSE will have to improve the efficiency of the testing and tracing chain, a process that may lead to people getting test results by text.
Any delay in tracing contacts can also lead to an explosion of infection he warned.
Dr Holohan added: “The World Health Organisation has advised that a likely future scenario in the dynamic of Covid-19 is recurring epidemic waves interspersed with periods of low-level transmission.
“This means that when Ireland eases social distancing restrictions, we may have periods of time when the numbers of people infected increases significantly.
“This is why it is vitally important that easing of social distancing restrictions is accompanied by a high level of adherence to the fundamental, individual behaviours needed to guard against transmission of the virus. We have to adapt our behaviours in order to live safely with Covid-19.”
The Chief Medical Officer stressed it was safe for people with non-Covid-19 illness to seek treatment in the country’s hospitals.
On Tuesday there were two new admissions to ICU where 86 patients continue to be treated.
There have been 6,393 healthcare workers infected with the disease.
There have been 857 deaths in residential care settings including 740 in nursing homes.
