Hypertrophic cardiomyopathy (HC) is probably the most common cause of sudden 
cardiac death in youthful athletes, and this diagnosis has represented a 
contraindication to continued participation in competitive sports. Less well 
appreciated is the fact that within the clinical spectrum of HC are patients 
who, despite having this disease, have been able to undertake particularly 
intensive and often extraordinary levels of training for sports competition over 
many years without dying suddenly. Fourteen such patients (13 men and 1 woman, 
aged 30 to 66 years [mean 43]) form the present study group. HC was initially 
identified at 24 to 57 years of age (mean 34), usually under fortuitous 
circumstances. Patients most often competed in distance running (including the 
marathon, 7), but also in swimming, triathalon, basketball, and football. The 
duration of training ranged from 6 to 22 years (mean 15) and 5 continue to train 
and compete actively. The magnitude of training, competition, and achievement 
was considerable in most patients; 12 of the 14 performed either at the 
national, collegiate or professional level in their sport, completed numerous 
marathon and triathalon events, or sustained particularly rigorous training 
regimens of > or = 50 miles/week. Echocardiographic studies demonstrated a left 
ventricular wall thickness of 18 to 28 mm (mean 20) in most patients (12 of 14) 
having a relatively localized pattern of ventricular septal hypertrophy. It is 
possible for some patients with HC to tolerate particularly intense athletic 
training and competition for many years, and even maintain high levels of 
achievement without incurring symptoms and disease progression or dying 
suddenly.(ABSTRACT TRUNCATED AT 250 WORDS)