GP sued after relying upon specialist's assessment

Was it unreasonable for the GP to accept the cardiologist's diagnosis of the condition causing his patient's upper-chest pain?

A 45-year-old man presented to his GP with a two-week history of intermittent, occasional throat and upper chest pain while bending over. His pain was not related to exertion. He smoked 20 cigarettes per day but had no past or family history of cardiac disease. 

The GP found no abnormality on examination. The patient was normotensive and was not obese. An ECG and a CXR were normal. The GP arranged immediate referral to a cardiologist for investigation and opinion.

The cardiologist saw the patient on two