Chief executives of the nation’s largest private health insurers are being called on to testify before a congressional hearing next month. On Wednesday, Democratic Congress member Dennis Kucinich of Ohio sent letters to firms including Aetna, CIGNA Corp, and UnitedHealth Group. Kucinich wants the insurance executives to appear before a House Oversight Subcommittee hearing on insurers’ coverage policies and claim denials. The request comes one week after Democratic Congress members Henry Waxman of California and Bart Stupak of Michigan asked firms to provide detailed financial information including salaries and profit margins.