A bicyclist who collapsed in San Geronimo Valley after developing a heart condition on Sunday was helped by an anonymous person who performed CPR, according to the Marin County Sheriff’s Office. Lt. Doug Pittman said the man, whose name was not released, was in improved condition and being treated in the intensive care unit at Marin General Hospital this week. Officials said the 53-year-old Sacramento-area man was traveling with his 14-year-old son, who bicycled ahead of him, when he collapsed on Nicasio Valley Road due to arrhythmia. The man was unconscious and not breathing when a citizen, who left before being identified, attempted to revive him. A sheriff’s deputy who responded to 911 calls from local residents also defibrillated the man.