An American couple vacationing in the Dominican Republic died of respiratory failure and pulmonary edema, according to officials.
Edward Nathaniel Holmes, 63, and Cynthia Ann Day, 49, were found dead Thursday in their hotel room at the Grand Bahia Principe La Romana Resort in San Pedro de Macoris on the southeast coast of the Dominican Republic.
(MORE: Delaware woman describes how she survived brutal attack during Dominican Republic vacation)They arrived at the hotel on May 25 and were scheduled to depart on Thursday, police said.
The couple was found dead after they missed their scheduled check-out time on Thursday, according to a statement from Bahia Principe Hotels & Resorts, which runs both oceanside destinations. Following protocol, hotel staff entered the room and found both Holmes and Day unresponsive, according to the statement.
Staff then contacted authorities, according to the hotel.
(Bodies of American family of 4 killed by gas poisoning in Mexico coming home for funeral: Relatives)Their bodies showed no signs of violence, police said. Several bottles of medicine used to treat high blood pressure were found in the couple's room, according to authorities. No other drugs were found.
It is unclear what led to the couple's deaths.
Their deaths were considered suspicious in part because Holmes complained of a pain on Thursday, but when a doctor arrived Holmes refused to see the doctor, police said.
Their cause of death was determined by autopsies performed at the Regional Institute of Forensic Sciences, police said. Officials are awaiting the toxicology and histopathology results.
The couple was from Prince George's County in Maryland, according to NBC Baltimore affiliate WBAL.
(MORE: American woman's murder in Costa Rica may have been sexually motivated: Officials)Photos that Holmes posted to Facebook on Tuesday show the couple beaming as they enjoyed an excursion out on the open water. "Boat ride of a lifetime!!!" reads the caption.
The U.S. Department of State confirmed the couple's deaths in a statement to ABC News.
"We offer our sincerest condolences to the family on their loss," a State Department official said. "We are in close contact with local authorities regarding their investigation into the cause of death. We stand ready to provide all appropriate consular assistance. The U.S. Department of State and our embassies and consulates abroad have no greater responsibility than the protection of U.S. citizens overseas. Out of respect to the family during this difficult time, we have no further comment."
The hotel said in a statement that it is "deeply saddened by the incident."
The news of the couple's death comes days after a Delaware woman described how she was brutally attacked by a man at her resort in Punta Cana six months ago.
ABC News' Conor Finnegan and Ben Gittleson contributed to this report.