IPVR is a rare clinical entity that was first diagnosed during life in 1955. In the past 35 years, only 69 patients have been reported. With increasing clinical awareness, as well as use of PDE, the confirmation of its clinical diagnosis has become easier and more accurate without having to take recourse to invasive cardiac studies as in the past. For this reason, it is becoming increasingly apparent that IPVR is not so rare as has been suggested in the past. IPVR is more common in men than in women, in whites than blacks, and in the young than the elderly. The mean age of IPVR patients is 27 years (range, 4 to 85). The majority of the patients are asymptomatic and the diagnosis is usually suspected upon the discovery of a crescendo-decrescendo, low-pitched, early to mid diastolic murmur in the second and third left intercostal space, which increases during inspiration, particularly in the presence of a hyperdynamic right ventricle and in the absence of peripheral circulatory phenomenon of aortic regurgitation. The ECG often shows right axis deviation, incomplete right bundle branch block, and rarely, right ventricular hypertrophy and strain. However, a normal ECG does not preclude its diagnosis. Approximately 30% of the IPVR patients have normal 12-lead ECGs. The diagnosis may be further suggested by the posteroanterior chest roentgenogram when dilated and large central pulmonary arteries are noted to pulsate vigorously (hilar dance) on chest fluoroscopy.(ABSTRACT TRUNCATED AT 250 WORDS)