A 70-year-old man was diagnosed with mid-ventricular obstructive hypertrophic cardiomyopathy (MVOHCM) with apical aneurysm and paradoxic jet flow. At cardiac catheterization, pressure study showed that there was a markedly high pressure-gradient of 90 mmHg between the apex and the base in systole. Apical pressure was 350 mmHg after premature ventricular contraction. The apical aneurysm was already dilated and spherical in late systole; the absence of active relaxation was considered to be the cause of the paradoxic jet flow. In this report, we suggest the pathogenesis of left ventricular apical aneurysm and paradoxic jet flow in MVOHCM.