Heart patient C. Clifton Mills was napping in his hospital bed at Johns Hopkins Tuesday when he was awakened by a sharp pain in his throat. As he bolted upright, a woman dressed in black walked away from his bed and out of his room, he told police.

Mills, 67, put his hand to his neck and discovered his throat had been slashed, police said. He called for a nurse, who notified security officers, but they were unable to find the woman.

Mills, a truck driver from Williamsport, in Washington County, told police he knew of no reason for anyone to try to harm him. His wound, which took nine stitches to close, did not delay his open heart surgery, which took place as scheduled today. Mills, recovering from that surgery, was listed in critical but stable condition.

The incident occurred at 2:15 p.m. Tuesday but was not reported to police until 5 1/2 hours later. Asked today about the delay, a hospital spokesman said, "Our security force was investigating at that time and trying to put all the pieces together."

Police said they interviewed another hospital patient who said he saw a woman enter Mills' room about 2:15 p.m. Both he and Mills said the woman had brown hair, was wearing a black coat and carrying a black bag and appeared to be between 30 and 35 years old, police said. Police said they are still searching for the woman.

Mills' mother, 88-year-old Minnie Mills of Williamsport, said her son, who is single, called home after the incident and told family members he was baffled by the assault. "She give him a quick slit, then run out," said Minnie Mills. "I never heard tell of such a thing."