OBJECTIVE--To describe the association of the Noonan's phenotype and a primary, familial non-hypertrophic cardiomyopathy with restrictive pathophysiology. DESIGN--Observational study. SETTING--Tertiary cardiac referral centre. PATIENTS--Affected family members. METHODS--Two generations of a single family were examined and a description of the clinical characteristics and electrocardiographic, echocardiographic, and haemodynamic data of those affected is given. RESULTS--Three family members have classic Noonan's phenotype and all have a non-dilated, non-hypertrophic cardiomyopathy. Inheritance is autosomal dominant but with variable penetrance. The electrocardiograms show increased left ventricular voltages in two patients. On echocardiography left ventricular wall and internal end diastolic dimensions are normal, and there is considerable bilateral atrial enlargement. Systolic function is moderately impaired in one patient and mildly impaired in another. Doppler echocardiography showed restrictive pathophysiology as an early end of left ventricular filling and considerable reversal of flow in the superior vena cava during atrial systole. CONCLUSION--Hypertrophic cardiomyopathy is well described in Noonan's syndrome. This is the first report of a non-hypertrophic cardiomyopathy with echocardiographic and haemodynamic features of restrictive pathophysiology.