Firefighters arrived at the property, close to the A77 in Ayr, at around 10:30pm on Tuesday after a member of the public called 999.
The blaze started when an electric heater in the bedroom set fire to nearby items of clothing.
Three adults were treated by paramedics for smoke inhalation and a hosereel jet was used to extinguish the flames.
Watch Manager Alan Gray, the incident commander, said: "This was a small fire within a bedroom and I committed two firefighters in breathing apparatus to extinguish it using a hosereel jet.
"They successfully contained the fire to the room where it originated but we requested an ambulance to provide precautionary check-ups to three adults who appeared to be suffering from slight smoke inhalation.
"It's important anyone who uses portable heaters keeps them away from clothing, curtains, bedding and furniture.
"A fire can spread incredibly quickly and even small fires produce potentially lethal smoke, so it's absolutely vital that every home is protected by working smoke alarms to give people early warning of the danger."