Caritas Christi Health Care, a six-hospital system owned by the Archdiocese of Boston, has announced it will make advanced cardiac care available at more of its community hospitals. The new program is called the Caritas Cardiovascular Network, under which several of the chain's community hospitals will offer onsite cardiac catheterization services. The network is also part of the strategy by Caritas Christi's new chief executive to turn around the financially strapped system.