Little information is available on the length of the systolic time intervals in adult patients with isolated ventricular septal defects (VSD). In the present study the external carotid pulse and the phono- and electrocardiogram were recorded in 17 patients, mean age 29 years, with angiographically proved VSD. They had unidirectional left-to-right shunts with ratios of pulmonary-to-systemic blood flow (Qp/Qs) of 1-5.22. Their right ventricular pressures were normal or only moderately elevated. Left ventricular ejection time was consistently abbreviated, the degree of abbreviation relating significantly with Qp/Qs (r = -0.70, p less than 0.01). The preejection period was prolonged but the relationship between its degree of prolongation and Qp/Qs did not reach statistical significance (r = 0.4), p greater than 0.05). The relationship between the preejection period/left ventricular ejection time ratio (PEP/LVET) and Qp/Qs was statistically significant (r = 0.51, p less than 0.05). We conlcude that in adult VSD patients with normal right ventricular pressures, a hemodynamically important shunting, i.e., Qp/Qs above 1.4 or left-to-right shunt exceeding 30% of pulmonary blood flow, may be excluded in the presence of a normal left ventricular ejection time or a normal PEP/LVET ratio.